JP7600406B2 - Anti-resonant preform with two contacts - Google Patents

Description

The present invention relates to an antiresonant element preform for producing an antiresonant hollow-core fiber.

Hollow-core fibers have a core with a vacuum cavity, which is filled with a gas or liquid. In hollow-core fibers, the interaction of light with the glass is smaller than in solid-core fibers. Since the refractive index of the core is smaller than that of the cladding, light guiding by total internal reflection is not possible. According to the physical mechanism of light guiding, hollow-core fibers are divided into "photonic bandgap fibers" and "antiresonant reflecting fibers".

In the case of a "photonic bandgap fiber", the hollow core region is surrounded by a cladding containing a periodic arrangement of small hollow ducts. The periodic structure in the cladding causes an effect called "photonic bandgap" in semiconductor technology, according to which light in a certain wavelength range scattered in the cladding structure constructively interferes due to Bragg reflection in the central cavity and cannot propagate laterally in the cladding.

In the case of an embodiment of a hollow-core fiber called an "anti-resonant hollow-core fiber" (ARHCF), the hollow-core region is surrounded by an inner cladding region inside which so-called "anti-resonant elements" (also "anti-resonant elements", or "AREs" for short) are located. The anti-resonant elements, uniformly distributed around the hollow-core wall, can operate at anti-resonance and act as a Fabry-Perot cavity that reflects the incident light that guides it through the fiber core.

This technology promises fibers with low optical attenuation, a very wide transmission spectrum (even in the UV or IR wavelength range), and low latency during data transmission.

From WO2020030894 A1, an anti-resonant hollow-core fiber is known, in which the core is surrounded by an inner cladding that contains non-resonant elements (also called "ARE"). These non-resonant elements serve to attenuate higher-order modes and have an ARE outer element and an ARE inner element inserted therein. The illustrated ARE inner element is designed in the shape of a plate. With this design, there is a risk that during elongation of the preform, the ARE inner element will come to rest on the inner wall of the cladding bore and therefore only the ARE outer element will ensure the attenuation of the higher-order modes, which will increase the attenuation overall.

From EP 3152607 A1 a further anti-resonant hollow core fibre is known, in which the ARE outer element and the ARE inner element are tubular in shape. The nested ARE outer element and the ARE inner element are in each case connected to one another along a connecting line and to the cladding tube. There is therefore a risk that the ARE elements undergo a rotational movement during extension, so that the uniformly distributed arrangement of the ARE elements on the inner wall of the cladding tube is disturbed, which is reflected in an increased attenuation.

Further aspects, for example, methods for producing ARE, are described in the following documents: CN 105807363 (B), WO 2015185761 (A1), WO 2017108061 (A1), WO 2018 169487 (A1), JP 2018150184 (A), and EP 3136143 (A1).

Preforms of a size that allows producing hundreds of kilometers of fiber are required for industrial use of antiresonant hollow-core fibers. This is the only way to make the cost of antiresonant hollow-core fibers more reasonable. In that respect, there are preforms that give good results on a laboratory scale but cannot be used for industrial production.

Anti-resonant hollow-core fibers, especially those containing nested structural elements, have complex internal geometries that make accurate and repeatable manufacturing even more difficult. This is even more true since they can only tolerate dimensional deviations less than the order of magnitude of the operating wavelength of the guided light in order to adhere to resonant or anti-resonant conditions, respectively. The construction of the fiber preform can cause deviations from the target geometry and can also be caused by unwanted, not-to-scale deformations during the fiber drawing process.

The object of the present invention is to provide an anti-resonant element preform that can be precisely positioned within an anti-resonant hollow-core fiber preform, particularly within a preform having a length greater than 1 m and an outer diameter greater than 40 mm, particularly greater than 90 mm.

In particular, the object of the present invention is to provide antiresonant hollow-core fiber preforms that can be produced in an accurate and reproducible manner despite their large volume, in particular lengths exceeding 1 m and outer diameters exceeding 40 mm, in particular exceeding 90 mm.

In particular, it is an object of the present invention to provide an anti-resonant hollow-core fiber preform that can be manufactured in an accurate and reproducible manner and that has low attenuation. In particular, it is an object of the present invention to provide an anti-resonant hollow-core fiber preform that efficiently attenuates higher order modes in the core while at the same time having low attenuation of the fundamental mode.

The object of the present invention is to identify an anti-resonant hollow-core fiber preform that can be manufactured in an accurate and reproducible manner and has low attenuation.

In particular, an object of the present invention is to provide an anti-resonant hollow-core fiber that efficiently attenuates higher-order modes.

The features of the independent claims contribute to at least partially achieving at least one of the above-mentioned objects. The dependent claims provide preferred embodiments that contribute to at least partially achieving at least one of the objects.

/1./An anti-resonant element preform for producing an anti-resonant hollow-core fiber, comprising:
A first longitudinal axis;
An ARE outer element formed in an arc shape and an ARE inner element,
the ARE outer element and the ARE inner element are connected to each other along two connecting lines arranged essentially parallel to the first longitudinal axis,
An anti-resonant element preform, characterized in that the ARE outer element has an inner space that is at least partially bounded by the ARE outer wall and into which the arc-shaped designed ARE inner element at least partially protrudes.

/2. /
the ARE outer element has a first circle radius R_outer;
2. The anti-resonant element preform of embodiment 1, wherein the ARE inner element has a second circular radius, R_inner.

/3. /
the ARE outer element has a first central angle α_outer;
3. The anti-resonance element preform of any one of claims 1 to 2, wherein the ARE inner element has a second central angle α_inner.

/4. /
The first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner);
The anti-resonant element preform has the following characteristics:
R_outer and R_inner are smaller than 12 mm, in particular smaller than 8 mm, in particular smaller than 5 mm;
R_outer and R_inner have at least one of: greater than 0.5 mm, in particular greater than 1 mm, in particular greater than 2 mm;
In particular, the first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner), and the anti-resonant element preform has the following characteristics:
R_outer and R_inner are smaller than 7 mm, in particular smaller than 6 mm;
An anti-resonant element preform according to embodiment 2 or 3, characterized in that R_outer and R_inner have at least one of: greater than 3 mm, in particular greater than 4 mm.

/5. /
The first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner);
The anti-resonant element preform has the following characteristics:
α_outer is smaller than 350°, particularly smaller than 345°, especially smaller than 340°,
α_outer is greater than 275°, especially greater than 295°, especially greater than 320°,
α_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
α_inner has at least one of the following: greater than 30°, in particular greater than 40°, in particular greater than 50°;
In particular, the at least one anti-resonant element has the following characteristics:
β_outer is smaller than 275°, in particular smaller than 260°, in particular smaller than 250°;
β_outer has at least one of the following: greater than 210°, in particular greater than 215°, in particular greater than 220°;
An anti-resonance element preform according to any one of embodiments 2 to 4, characterized in that the sum of β_outer and β_inner has a value of 360°.

/6. /The anti-resonant element preform is
Greater than 1.1, especially greater than 1.5, especially greater than 1.6, especially greater than 1.7,
An anti-resonant element preform described in any one of embodiments 3 to 5, characterized in that it has a preform bow ratio smaller than 5.5, particularly smaller than 5, particularly smaller than 4, particularly smaller than 3, particularly smaller than 2.8, particularly smaller than 2.5.

/7./An anti-resonant element preform according to any one of embodiments 4 to 6, characterized in that the amount of deviation of the first circle radius R_outer from the second circle radius R_inner is less than 5% of the first circle radius R_outer, in particular less than 3%, in particular less than 2%, in particular less than 1.5%, in particular less than 1%.

/8. /
The first circle radius R_outer is greater than the second circle radius R_inner (R_outer>R_inner);
The anti-resonant element preform has the following characteristics:
R_outer is smaller than 12 mm, particularly smaller than 8 mm, especially smaller than 5 mm;
R_outer is greater than 0.5 mm, especially greater than 1 mm, especially greater than 2 mm,
R_inner is smaller than 8 mm, in particular smaller than 5 mm, in particular smaller than 3 mm;
An anti-resonant element preform according to any one of the preceding embodiments, characterized in that R_inner is greater than 0.5 mm, in particular greater than 0.75 mm, in particular greater than 1 mm.

/9. /
The first circle radius R_outer is greater than the second circle radius R_inner (R_outer>R_inner);
The anti-resonant element preform has the following characteristics:
α_outer is smaller than 350°, particularly smaller than 345°, especially smaller than 340°,
α_outer is greater than 275°, especially greater than 295°, especially greater than 320°,
α_inner is smaller than 300°, in particular smaller than 285°, in particular smaller than 230°;
The anti-resonant element preform according to any one of the preceding embodiments, characterized in that α_inner has at least one of the following: greater than 100°, in particular greater than 120°, in particular greater than 150°.

/10. /
The first circle radius R_outer is smaller than the second circle radius R_inner (R_outer<R_inner);
The anti-resonant element preform has the following characteristics:
R_outer is smaller than 12 mm, particularly smaller than 8 mm, especially smaller than 5 mm;
R_outer is greater than 0.5 mm, especially greater than 1 mm, especially greater than 2 mm,
R_inner is smaller than 20 mm, in particular smaller than 10 mm, in particular smaller than 8 mm,
An anti-resonant element preform according to any one of the preceding embodiments, characterized in that R_inner is greater than 1 mm, in particular greater than 2 mm, in particular greater than 3 mm.

/11. /
The first circle radius R_outer is smaller than the second circle radius R_inner (R_outer<R_inner);
The anti-resonant element preform has the following characteristics:
α_outer is smaller than 340°, particularly smaller than 315°, particularly smaller than 305°,
α_outer is greater than 200°, particularly greater than 220°, particularly greater than 250°,
α_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
An anti-resonant element preform according to any one of embodiments 1 to 3 or 10, characterized in that α_inner has at least one of the following: greater than 30°, in particular greater than 40°, in particular greater than 50°.

/12. /
The anti-resonance element preform according to any one of embodiments 3 to 11, wherein the first central angle α_outer and/or the second central angle α_inner is smaller than 340°.

/13. /
The ARE outer element has a first segment height, H_outer;
The ARE inner element has a second segment height H_inner, in particular
the ratio of the first segment height H_outer to the second segment height H_inner (H_outer/H_inner) is less than 30, in particular less than 14, in particular between 1 and 6;
especially,
H_outer/H_inner is less than 15, in particular less than 14, in particular less than 10, in particular less than 6.5, in particular less than 4, in particular less than 3.2;
An anti-resonant element preform according to any one of the preceding embodiments, characterized in that H_outer/H_inner is greater than 1.7, in particular greater than 1.75, in particular greater than 1.85.

/14. An anti-resonant element preform according to any one of embodiments 1 to 13, characterized in that the ARE arc element is disposed in the inner space of the ARE outer element, and in particular, the ARE arc element is disposed in the ARE inner element.

/15. /An anti-resonant element preform according to claim 14, characterized in that the ARE arc element comprises an amorphous solid, in particular glass, in particular quartz glass, in particular consists of an amorphous solid, in particular glass, in particular quartz glass, in particular the ARE arc element and the ARE outer element are made of the same material.

/16. The /ARE arc element is designed in a circular arc shape and has a fifth circle radius R_arc and a fifth central angle α_arc;
16. The anti-resonant element preform of embodiment 14 or 15, wherein the ARE arc element is connected to the ARE outer element and/or the ARE inner element along two contact lines.

/17. The /ARE arc element is designed to be circular and has a radius R_circle;
16. The anti-resonance element preform of claim 14 or 15, wherein the ARE arc element is connected to the ARE inner element along a contact line.

/18. /An anti-resonant hollow-core fiber preform, comprising:
a cladding tube having a cladding bore and a cladding longitudinal axis along which extends a cladding wall bounded by an inner surface and an outer surface;
a number of anti-resonant element preforms;
The anti-resonant element preforms are disposed at target positions on the inner surface of the cladding tube wall in a spaced relationship with each other and in a non-contact manner;
17. A preform, wherein at least one of the anti-resonant element preforms is designed according to any one of embodiments 1 to 16.

/19. /The anti-resonant element preform is
Greater than 1.1, especially greater than 1.5, especially greater than 1.6, especially greater than 1.7,
A preform as described in embodiment 18, characterized in that it has a preform bow ratio of less than 5.5, particularly less than 5, particularly less than 4, particularly less than 3, particularly less than 2.8, particularly less than 2.5.

/20./The ratio z/R_preform is
Greater than 0.1, especially greater than 0.2, especially greater than 0.25,
A preform according to embodiment 18 or 19, characterized in that it is smaller than 1, in particular smaller than 0.8, in particular smaller than 0.5.

/21./A preform according to any one of embodiments 18 to 20, characterized in that for each anti-resonant element preform, the amount of deviation of the first circle radius R_outer from the second circle radius R_inner is less than 5% of the first circle radius R_outer, in particular less than 3%, in particular less than 2%, in particular less than 1.5%, in particular less than 1%.

/22./A method for manufacturing an anti-resonant hollow-core fiber preform, comprising the steps of:
a) providing a cladding tube having a cladding tube bore and a cladding tube longitudinal axis along which extends a cladding tube wall bounded by an inner surface and an outer surface;
b) preparing several anti-resonant element preforms, each including an ARE outer element and an ARE inner element inserted therein;
c) placing the anti-resonant element preform at a target location within the cladding tube bore;
d) treating the assembly including the cladding tube and the anti-resonant element preform by a hot forming process, selected from at least one of stretching and crushing;
A relative internal pressure in the range of -10 to -300 mbar, in particular -50 to -250 mbar, is set in the cladding bore in step d) "treatment",
The ARE outer element and the ARE inner element are designed in an arc shape in at least one anti-resonant element preform;
A method in which the ARE outer element and the ARE inner element are connected to each other and to the cladding tube bore along two connecting lines.

23. The method according to embodiment 22, characterized in that the ARE outer element has an inner space bounded by the ARE outer wall and into which the arc-shaped designed ARE inner element at least partially projects.

/24. The ARE outer element has a first central angle α_outer and the ARE inner element has a second central angle α_inner;
The method of embodiment 22 or 23, wherein the first central angle α_outer and/or the second central angle α_inner is greater than 340°.

/25./The method according to any one of embodiments 22 to 24, characterized in that the anti-resonant element preform is thermally fixed to the cladding tube wall in the absence of flame in step f) "treatment".

26. The method according to any one of the embodiments 22 to 25, characterized in that the cladding tube has an outer diameter in the range of 65 to 300 mm, in particular 90 to 250 mm, and in particular a length of at least 1 m.

/27./A method of producing a secondary preform from which an anti-resonant hollow-core fiber can be drawn from a preform produced according to any one of the preceding embodiments 18 to 21, comprising the steps of:
further processing the preform into a secondary preform;
Further processing steps include the following hot forming process:
i.) elongate;
ii.) crushing;
iii.) crush and stretch simultaneously;
iv.) adding additional coating material;
v.) adding additional coating material followed by stretching;
vi.) adding additional coating material and simultaneously stretching;
The method includes performing one or several of the steps one or more times.

28. The method of any one of claims 22 to 27, wherein at least one of the anti-resonant element preforms is designed according to any one of claims 1 to 17.

/29./An anti-resonant hollow-core fiber,
a cladding having an inner cladding bore and a longitudinal axis along which extends a cladding wall bounded by an inner cladding surface and an outer cladding surface;
several anti-resonant elements, each of which comprises an ARE outer unit and an ARE inner unit, the ARE outer unit designed in an arc shape and the ARE inner unit being connected to each other along two seam lines;
The anti-resonant elements are arranged at target positions on the inner surface of the cladding wall in a spaced-apart, non-contact manner;
an ARE outer unit having an inner space at least partially bounded by an ARE outer wall and into which an ARE inner unit designed in an arc shape at least partially protrudes.

/30./An anti-resonant hollow-core fiber according to embodiment 29, characterized in that the anti-resonant hollow-core fiber has 3, 4, 5, 6, 7, or 8 anti-resonant elements, in particular, the anti-resonant hollow-core fiber has an odd number of anti-resonant elements.

/31./Anti-resonant hollow-core fibers have the following characteristics:
The anti-resonant elements are arranged symmetrically on the inner surface of the cladding wall.
at least one of the ARE outer unit and/or the ARE inner unit is made of an amorphous solid, in particular of glass, in particular of quartz glass, in particular of glass having a refractive index of at least 1.4, in particular from 1.4 to 3, in particular from 1.4 to 2.8;
The anti-resonant hollow-core fiber of any one of embodiments 29 or 30, characterized in having at least one of the following: the wall thicknesses of the ARE outer unit and the ARE inner unit are essentially identical.

/32./Anti-resonant hollow-core fibers have the following characteristics:
Basic attenuation of less than 0.15 dB/km at transmission wavelengths of 1.0 to 2.5 μm;
32. The anti-resonant hollow-core fiber of any one of embodiments 29 to 31, characterized in that it has at least one of the following: a fundamental attenuation of less than 1 dB/km at transmission wavelengths up to 0.8 μm.

/33./An anti-resonant hollow-core fiber according to any one of embodiments 29 to 32, characterized in that the anti-resonant element forms a core having a core radius smaller than 50 μm, in particular smaller than 40 μm, in particular smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 20 μm, in particular smaller than 15 μm, in particular smaller than 13 μm.

/34./Anti-resonant hollow-core fibers have the following characteristics:
The ARE outer unit includes a third circle radius FB_outer;
The ARE inner unit includes a fourth circle radius FB_inner;
The ARE outer unit includes a third central angle β_outer;
The anti-resonant hollow-core fiber of any one of embodiments 29 to 33, wherein the ARE inner unit has at least one of the following: a fourth central angle β_inner.

/35. /
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 15 μm;
FB_outer is greater than 5 μm, in particular greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 15 μm;
An anti-resonant hollow-core fiber as described in embodiment 34, characterized in that FB_inner has at least one of the following: greater than 5 μm, in particular greater than 10 μm, in particular greater than 12 μm.

/36. /
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 25 μm, in particular smaller than 22 μm, in particular smaller than 17 μm, in particular smaller than 16 μm;
FB_outer is greater than 5 μm, in particular greater than 7 μm, in particular greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 25 μm, in particular smaller than 22 μm, in particular smaller than 20 μm, in particular smaller than 17 μm, in particular smaller than 16 μm;
An anti-resonant hollow-core fiber according to embodiment 34 or 35, characterized in that FB_inner has at least one of the following: greater than 5 μm, in particular greater than 7 μm, in particular greater than 10 μm, in particular greater than 12 μm.

/37. /
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
Anti-resonant elements have the following characteristics:
FB_outer is 16.5 μm or less, particularly 15.75 μm or less;
FB_outer is 11.5 μm or more, particularly 12.25 μm or more;
FB_inner is 16.5 μm or less, in particular 15.75 μm or less;
37. The anti-resonant hollow-core fiber of any one of embodiments 34 to 36, characterized in that FB_inner is 11.5 μm or more, in particular 12.25 μm or more.

/38. /
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
At least one anti-resonant element has the following characteristics:
β_outer is smaller than 350°, in particular smaller than 345°, in particular smaller than 340°;
β_outer is greater than 275°, in particular greater than 295°, in particular greater than 320°,
β_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
An anti-resonant hollow-core fiber according to any one of embodiments 34 to 37, characterized in that β_inner has at least one of the following: β_inner is greater than 30°, in particular greater than 40°, in particular greater than 50°.

/39. /At least one anti-resonant element has the following characteristics:
β_outer is smaller than 275°, in particular smaller than 260°, in particular smaller than 250°;
β_outer has at least one of the following: greater than 210°, in particular greater than 215°, in particular greater than 220°;
An anti-resonant hollow-core fiber according to any one of embodiments 34 to 38, wherein the sum of β_outer and β_inner has a value of 360°.

/40. /At least one anti-resonant element has the following characteristics:
A bow ratio greater than 1.5, especially greater than 1.55, especially greater than 1.6,
a bow ratio of less than 3.2, in particular less than 2.8, in particular less than 2.5;
40. The anti-resonant hollow-core fiber of any one of embodiments 29 to 39, in particular characterized by a confinement loss of the fundamental mode less than 10E-2 db/m.

/41. /The ratio z/R is
greater than 0.6, especially greater than 0.7, especially greater than 0.8,
An anti-resonant hollow-core fiber according to any one of embodiments 29 to 40, characterized in that it is smaller than 1.4, in particular smaller than 1.3, in particular smaller than 1.2.

/42./An antiresonant hollow-core fiber according to any one of embodiments 35 to 41, characterized in that the amount of deviation of the third circle radius FB_outer from the fourth circle radius is less than 5% of the third circle radius FB_outer, in particular less than 3%, in particular less than 2%, in particular less than 1.5%, in particular less than 1%.

/43. /
● FB_outer> FB_inner,
At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 15 μm;
FB_outer is greater than 5 μm, in particular greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 20 μm, in particular smaller than 15 μm, in particular smaller than 11 μm;
An anti-resonant hollow-core fiber as described in embodiment 29, characterized in that FB_inner has at least one of the following: greater than 2 μm, in particular greater than 4 μm, in particular greater than 6 μm.

/44. /
● FB_outer> FB_inner,
At least one anti-resonant element has the following characteristics:
β_outer is smaller than 350°, in particular smaller than 345°, in particular smaller than 340°;
β_outer is greater than 275°, in particular greater than 295°, in particular greater than 320°,
β_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
The anti-resonant hollow-core fiber of embodiment 29 or 43, characterized in that β_inner has at least one of the following: β_inner is greater than 30°, in particular greater than 40°, in particular greater than 50°.

/45. /
● FB_outer < FB_inner,
At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 15 μm;
FB_outer is greater than 5 μm, in particular greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 20 μm, in particular smaller than 15 μm, in particular smaller than 11 μm;
An anti-resonant hollow-core fiber as described in embodiment 29, characterized in that FB_inner has at least one of the following: greater than 2 μm, in particular greater than 4 μm, in particular greater than 6 μm.

/46. /
● FB_outer < FB_inner,
At least one anti-resonant element has the following characteristics:
β_outer is smaller than 340°, in particular smaller than 315°, in particular smaller than 305°;
β_outer is greater than 200°, in particular greater than 220°, in particular greater than 250°,
β_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
The anti-resonant hollow-core fiber of embodiment 29 or 45, characterized in that β_inner has at least one of the following: β_inner is greater than 30°, in particular greater than 40°, in particular greater than 50°.

/47./An antiresonant hollow-core fiber according to any one of embodiments 34 to 46, characterized in that the third central angle β_outer and/or the fourth central angle β_inner are greater than 340°.

/48. /
The ARE outer unit has a third segment height HF_outer and the ARE inner unit has a fourth segment height H_inner, in particular:
An anti-resonant hollow-core fiber according to any one of embodiments 29 to 47, characterized in that HF_outer/HF_inner<30.

/49. /At least one anti-resonant element has the following characteristics:
HF_outer/HF_inner is less than 6.5, especially less than 4, especially less than 3.2;
An anti-resonant hollow-core fiber as described in embodiment 48, characterized in that HF_outer/HF_inner has at least one of the following: HF_outer/HF_inner is greater than 1.7, in particular greater than 1.75, in particular greater than 1.85.

/50. An anti-resonant hollow-core fiber according to any one of embodiments 29 to 49, characterized in that the ARE arc unit is disposed within the ARE outer unit.

/51./An antiresonant hollow-core fiber according to any one of embodiments 29 to 50, characterized in that the basic attenuation difference between a straight antiresonant hollow-core fiber and an antiresonant hollow-core fiber wound to a diameter of 10 mm is two orders of magnitude smaller, in particular an order of magnitude smaller, in particular less than half an order of magnitude.

/52. The wall thickness of the ARE outer unit and/or the ARE inner unit is 0.25 μm to 0.75 μm, in particular 0.35 μm to 0.65 μm, in particular 0.5 μm;
In particular, the wall thickness of the ARE-outer unit and/or the ARE-inner unit is between 0.35 μm and 0.65 μm, in particular between 0.4 μm and 0.6 μm, in particular 0.5 μm, at a signal wavelength of 1550 nm in the first transmission window;
An anti-resonant hollow-core fiber according to any one of embodiments 29 to 51, characterized in that in particular the wall thickness of the ARE-outer unit and/or the ARE-inner unit is between 1.25 μm and 0.75 μm, in particular between 1.1 μm and 0.9 μm, in particular 1 μm, at a signal wavelength of 1550 nm in the second transmission window.

/53./An anti-resonant hollow-core fiber according to any one of embodiments 29 to 52, characterized in that the anti-resonant hollow-core fiber is manufactured from a preform according to any one of embodiments 18 to 21.

/54./An anti-resonant hollow-core fiber according to any one of embodiments 29 to 53, characterized in that the anti-resonant hollow-core fiber is manufactured according to the method according to any one of embodiments 22 to 28.

/55. / A method for producing an anti-resonant hollow-core fiber from a preform according to any one of embodiments 18 to 21, in particular produced according to the method according to any one of embodiments 22 to 28, comprising:
further processing the preform into an anti-resonant hollow-core fiber;
Further processing steps include the following hot forming process:
i.) elongate;
ii.) crushing;
iii.) crush and stretch simultaneously;
iv.) adding additional coating material;
v.) adding additional coating material followed by stretching;
vi.) adding additional coating material and simultaneously stretching;
The present invention includes one or several of the above steps performed once or repeatedly.

/56. The method of embodiment 56, characterized in that a relative internal pressure in the range of 0.05 mbar to 20 mbar is established in the core region in the step "further processing" as part of elongating the preform into an anti-resonant hollow-core fiber.

Some of the described features are associated with the term "essentially". The term "essentially" should be understood such that under practical conditions and manufacturing techniques, mathematically strict interpretations of terms such as "overlap", "perpendicular", "diameter", or "parallelism" cannot be strictly performed, but only within certain manufacturing-related error tolerances. For example, "essentially parallel axes" describe angles between -5 degrees and 5 degrees with respect to each other, and "essentially the same volume" includes deviations of up to 5% by volume. For example, a "device consisting essentially of quartz glass" includes a quartz glass portion of more than 95% by weight and less than 100% by weight. Furthermore, "essentially perpendicular" includes angles of 85 degrees to 95 degrees. Further clarification of the term "essentially" for some features is provided below.

The above object is solved by an anti-resonant element preform for manufacturing an anti-resonant hollow-core fiber, comprising a first longitudinal axis, an ARE outer element designed in an arc shape, and an ARE inner element, the ARE outer element and the ARE inner element being connected to each other along two connecting lines arranged essentially parallel to the first longitudinal axis. According to the invention, it is provided that the ARE outer element has an inner space that is at least partially limited by the ARE outer wall and into which the ARE inner element designed in an arc shape at least partially protrudes.

The antiresonant element preform designed in this way and its use in a preform for an antiresonant hollow-core fiber has the advantage, compared to known antiresonant element preforms, that an additional degree of freedom is provided by the arc-shaped design of the ARE inner element. There are no longer any limitations when selecting the radius of the ARE inner element, which can in particular be larger than the radius of the ARE outer element.

The antiresonant element preform constructed in this way can be manufactured separately from the further components for manufacturing the antiresonant hollow-core fiber, which is advantageous from a manufacturing-related aspect. Antiresonant element preforms that differ from the ideal structure, for example during manufacturing, can therefore be discarded relatively cheaply and without the need to discard further components for manufacturing the antiresonant hollow-core fiber. By pre-manufacturing the antiresonant element preforms, further uniformity can be achieved over the entire manufacturing batch, which has an advantageous effect on the symmetry of the preforms manufactured with the antiresonant element preforms and ultimately of the antiresonant hollow-core fiber. Increasing the symmetry has a positive effect on the optical properties of the hollow-core fiber.

Compared to the prior art anti-resonant element preforms, the anti-resonant element preforms according to the present invention:
The ARE outer and inner elements have negative curvature, which has a positive effect on damping;
- Characterized in that virtually any combination of radii of the ARE inner and outer elements is possible thanks to the options offered according to the invention.

This additional degree of freedom provides improved mode matching in the subsequent antiresonant hollow-core fiber.

In the context of the present invention, the term "arc" is understood to be a portion of a circumference. Two points on a circle divide the circumference into two arcs. Direct connection of the two points generates a line segment called a chord. Connecting the two points to the center of the circle by a line segment each results in two separate circle parts (also called sectors). A sector is therefore pseudo-cut out of the circle by two radii. The part of the circumference that belongs to a sector is called an arc and the angle between the two radii is called the central angle. There is exactly one central angle for each arc. The sum of all the central angles in a circle is 360°.

In the context of the present invention, the term arcuately designed ARE outer element and/or ARE inner element is understood to mean tubularly designed elements having a cross section corresponding to a circular arc along their respective longitudinal axes.

In the context of the present invention, the term relating to the inner space of an ARE outer element designed in an arc refers to the space enclosed by the arc and the chord.

In the context of the present invention, the statement that the ARE inner element, designed in an arc, projects into the inner space of the ARE outer element is understood to mean that the arc of the ARE inner element passes essentially above the chord of the ARE outer element.

The term "essentially parallel" should be understood such that under practical conditions and manufacturing techniques, mathematically exact parallelism cannot be reached, but can only be provided within certain manufacturing-related error tolerances. Thus, the term "essentially parallel" is understood to be an angle between two axes of -5 degrees to 5 degrees with respect to each other.

In one embodiment, the first longitudinal axis of the connection line is designed to be parallel such that at least one of the connection lines and the first longitudinal axis, in particular both the connection line and the first longitudinal axis, have an angle of -1.5 degrees to 1.5 degrees, preferably -0.85 degrees to 0.85 degrees, preferably -0.42 degrees to 0.42 degrees with respect to each other. This parallelism ensures that the anti-resonant element preform efficiently damps higher order modes and further ensures compliance with the resonance or anti-resonance conditions, respectively, in the subsequent hollow core fiber.

In one embodiment, the antiresonant element preform comprises or consists of a material transparent to the operating light of the optical fiber, for example glass, in particular doped or undoped quartz glass (SiO2). The doping provides for matching of physical properties, for example the thermal expansion coefficient. Fluorine, chlorine and/or hydroxyl groups are preferably used as doping agents to reduce the viscosity of the quartz glass.

Based on the arc design, the ARE outer element and the ARE inner element are connected to each other along two connecting lines arranged essentially parallel to the first longitudinal axis.

In a two-dimensional diagram, the bonds for the connecting lines in each case are
a first end point of the ARE exterior wall of the ARE exterior element;
- Between the second end point of the wall of the ARE inner element.

During assembly of the anti-resonant element preform at its target position in the cladding tube bore (see step c) "Placement" and/or step d) "Processing"), material-to-material bonding of these connection lines to the inner surface of the cladding tube wall is performed. In cross section, the anti-resonant element preform is connected to the cladding tube bore at two points. On the one hand, the connection at two points in cross section increases the assembly precision of the anti-resonant element preform in the cladding tube. On the other hand, the risk of rotational movements of the anti-resonant element preform and/or the ARE outer element and/or the ARE inner element during stretching and/or crushing is reduced. This increases the precision of the preform and of the anti-resonant hollow-core fiber produced by the preform and thus having lower attenuation.

In the case of preforms from the prior art, due to the fact that the ARE inner element is designed in a plate-like manner, there is a risk that during elongation into the ARE inner unit in the antiresonant hollow-core fiber, the ARE inner element will position itself against the inner wall of the cladding tube inner bore, and therefore only the ARE outer unit will ensure an antiresonant behavior that increases the attenuation. In the case of the embodiments described here, the design of the ARE inner element reduces the risk that the ARE inner element will be crushed and/or deformed during elongation, which in particular leads to variations in the wall thickness of the ARE inner element and/or the ARE inner unit, which leads to an increase in attenuation in the subsequent antiresonant hollow-core fiber. Thus, the antiresonant element and/or the ARE inner unit and/or the antiresonant hollow-core fiber designed in this way achieves an improved mode match.

One embodiment of the anti-resonant element preform is characterized in that the ARE outer element has a first circular radius R_outer and the ARE inner element has a second circular radius R_inner.

One embodiment of the anti-resonant element preform is characterized in that the ARE outer element has a first central angle α_outer and the ARE inner element has a second central angle α_inner.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner);
The anti-resonant element preform has the following characteristics:
R_outer and R_inner are smaller than 12 mm, in particular smaller than 8 mm, in particular smaller than 5 mm;
R_outer and R_inner have one of the following characteristics: greater than 0.5 mm, in particular greater than 1 mm, in particular greater than 2 mm.

In this alternative embodiment, the degrees of freedom afforded by the present invention are used such that the first circular radius R_outer of the ARE outer element and the second circular radius R_inner of the ARE inner element are essentially the same length.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner);
The anti-resonant element preform has the following characteristics:
R_outer and R_inner are smaller than 7 mm, in particular smaller than 6 mm;
R_outer and R_inner are characterized in having at least one of the following: greater than 3 mm, in particular greater than 4 mm.

In the context of the present invention, the statement that two lengths, e.g. a first circle radius R_outer and a second circle radius R_inner, are "essentially" the same length is to be understood as the lengths being the same within manufacturing-related tolerances, in particular the lengths differing by less than 5%, in particular less than 3%, in particular less than 2%. Thus, one embodiment is characterized in that the amount of deviation of the first circle radius R_outer from the second circle radius R_inner is less than 5%, in particular less than 3%, in particular less than 2%, in particular less than 1.5%, in particular less than 1%, in particular less than 0.5% of the first circle radius R_outer.

Due to the identical length of the first circle radius R_outer and the second circle radius R_inner, the ARE outer element and the ARE inner element have essentially identical negative curvatures, which positively impacts the attenuation in the anti-resonant hollow-core fiber for fiber lengths greater than 20 km. In particular, particularly accurate and consistent production of industrially usable preforms with lengths greater than 1 m and outer diameters greater than 40 mm, especially greater than 90 mm, is possible.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner);
The anti-resonant element preform has the following characteristics:
α_outer is smaller than 350°, particularly smaller than 345°, especially smaller than 340°,
α_outer is greater than 275°, especially greater than 295°, especially greater than 320°,
α_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
- α_inner is characterized in having at least one of the following: greater than 30°, in particular greater than 40°, in particular greater than 50°.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner);
Applied to anti-resonant element preforms are:
α_outer is smaller than 275°, particularly smaller than 260°, particularly smaller than 250°,
α_outer has at least one of the following: greater than 210°, in particular greater than 215°, in particular greater than 220°;
The sum of α_outer and α_inner has a value of 360°.

By correspondingly selecting the first central angle α_outer and the second central angle α_inner, lower attenuation can also be achieved in case of strong curvature of the anti-resonant hollow-core fiber under the boundary condition that the first circle radius R_outer and the second circle radius R_inner are essentially of the same length.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer is greater than the second circle radius R_inner (R_outer>R_inner);
The anti-resonant element preform has the following characteristics:
R_outer is smaller than 12 mm, particularly smaller than 8 mm, especially smaller than 5 mm;
R_outer is greater than 0.5 mm, especially greater than 1 mm, especially greater than 2 mm,
R_inner is smaller than 8 mm, in particular smaller than 5 mm, in particular smaller than 3 mm;
R_inner is characterized in having at least one of the following: greater than 0.5 mm, in particular greater than 0.75 mm, in particular greater than 1 mm.

In this alternative embodiment, the degrees of freedom afforded by the present invention are used to make the first circular radius R_outer of the ARE outer element larger than the second circular radius R_inner of the ARE inner element. This results in lower attenuation of the anti-resonant hollow-core fiber produced from the preform.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer is greater than the second circle radius R_inner (R_outer>R_inner);
The anti-resonant element preform has the following characteristics:
α_outer is smaller than 350°, particularly smaller than 345°, especially smaller than 340°,
α_outer is greater than 275°, especially greater than 295°, especially greater than 320°,
α_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
- α_inner is characterized in having at least one of the following: greater than 30°, in particular greater than 40°, in particular greater than 50°.

By correspondingly selecting the first central angle α_outer and the second central angle α_inner, low attenuation of the anti-resonant hollow-core fiber can be achieved under the boundary condition that the first circle radius R_outer is greater than the second circle radius R_inner.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer is smaller than the second circle radius R_inner (R_outer<R_inner);
The anti-resonant element preform has the following characteristics:
R_outer is smaller than 12 mm, particularly smaller than 8 mm, especially smaller than 5 mm;
R_outer is greater than 0.5 mm, especially greater than 1 mm, especially greater than 2 mm,
R_inner is smaller than 20 mm, in particular smaller than 10 mm, in particular smaller than 8 mm,
R_inner is characterized in having at least one of the following: greater than 1 mm, in particular greater than 2 mm, in particular greater than 3 mm.

In this alternative embodiment, the degrees of freedom afforded by the invention are used such that the first circle radius R_outer of the ARE outer element is smaller than the second circle radius R_inner of the ARE inner element. This type of design provides a particularly simple type of modal adaptation.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer is smaller than the second circle radius R_inner (R_outer<R_inner);
The anti-resonant element preform has the following characteristics:
α_outer is smaller than 340°, particularly smaller than 315°, particularly smaller than 305°,
α_outer is greater than 200°, especially greater than 220°, especially greater than 250°,
α_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
- α_inner is characterized in having at least one of the following: greater than 30°, in particular greater than 40°, in particular greater than 50°.

By correspondingly selecting the first central angle α_outer and the second central angle α_inner, low attenuation of the anti-resonant hollow-core fiber can be achieved.

One embodiment of the anti-resonant element preform is characterized in that the first central angle α_outer and/or the second central angle α_inner is smaller than 350°, in particular the first central angle α_outer and/or the second central angle α_inner is [110°; 310°], in particular [120°; 290°], in particular [150°; 280°].

One embodiment of the anti-resonant element preform comprises:
The first central angle α_outer is greater than 270° and less than 350°;
The second central angle α_inner is greater than 160° and less than 300°.
In particular, the first central angle α_outer is greater than 280° and less than 340°;
The second central angle α_inner is characterized in that it is greater than 210° and smaller than 290°.

By corresponding selection of the first central angle α_outer and/or the second central angle α_inner, low attenuation of the anti-resonant hollow-core fiber can be achieved.

One embodiment of the anti-resonant preform comprises:
the first central angle α_outer is smaller than 275°, in particular smaller than 260°, in particular smaller than 250°;
The first central angle α_outer is greater than 210°, in particular greater than 215°, in particular greater than 220°;
The second central angle α_inner results from the difference between α_outer and 360°,
The sum of α_outer and β_inner has a value of 360°.

One embodiment of the anti-resonant element preform is characterized in that the ARE outer element has a first segment height H_outer and the ARE inner element has a second segment height H_inner, and in particular:
H_outer/H_inner is less than 30, especially less than 14, especially between 1 and 6.

The first segment height H_outer refers to the distance from the apex of the ARE outer element to the first chord. The second segment height H_inner refers to the distance from the apex of the ARE inner element to the second chord. In this embodiment, the risk of the ARE inner element deforming during crushing and/or stretching is reduced, which subsequently increases the attenuation of the anti-resonant hollow-core fiber.

One embodiment of the anti-resonant element preform is characterized in that the ARE outer element has a first segment height H_outer and the ARE inner element has a second segment height H_inner, where:
H_outer/H_inner is less than 15, in particular less than 14, in particular less than 10, in particular less than 6.5, in particular less than 4, in particular less than 3.2;
H_outer/H_inner is greater than 1.7, in particular greater than 1.75, in particular greater than 1.85.

The preform bow ratio is defined as follows:

The preform bow ratio therefore specifies the ratio of the two central angles of the ARE element (and thus the ARE outer element and the ARE inner element) to each other.

One embodiment of the anti-resonant element preform has a preform bow ratio of:
Greater than 1.1, especially greater than 1.5, especially greater than 1.6, especially greater than 1.7,
- Characterized by a preform bow ratio smaller than 5.5, in particular smaller than 5, in particular smaller than 4, in particular smaller than 3, in particular smaller than 2.8, in particular smaller than 2.5.

One embodiment of the anti-resonant element preform comprises:
The first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner);
The anti-resonant element preform is
Greater than 1.1, especially greater than 1.5, especially greater than 1.6, especially greater than 1.7,
- Characterized by a preform bow ratio smaller than 5.5, in particular smaller than 5, in particular smaller than 4, in particular smaller than 3, in particular smaller than 2.8, in particular smaller than 2.5.

In this embodiment, the anti-resonant element preform can be integrated in a particularly precise manner into the preform, in particular into preforms having a length of more than 1 m and an outer diameter of more than 40 mm, in particular more than 90 mm.

One embodiment of the anti-resonant element preform is characterized in that the ARE arc element is disposed in the inner space of the ARE outer element, and in particular, the ARE arc element is disposed in the ARE inner element.

The ARE arc elements serve to attenuate undesired modes. Corresponding integration of the antiresonant element into the preform can further facilitate mode matching of the preform and/or subsequent antiresonant hollow-core fiber.

In one embodiment, the ARE arc element comprises or consists of a material transparent to the operating light of the optical fiber, for example glass, in particular doped or undoped quartz glass (SiO2), or an amorphous solid. The doping provides for matching of physical properties, for example the thermal expansion coefficient. Fluorine, chlorine and/or hydroxyl groups are preferably used as doping agents to reduce the viscosity of the quartz glass. The ARE arc element and the ARE outer element may in particular be made of the same material.

One embodiment of the anti-resonant element preform is characterized in that the ARE arc element is designed in an arc shape, has a fifth circle radius R_arc and a fifth central angle α_arc, and is connected to the ARE outer element and/or the ARE inner element along two contact lines.

One embodiment of the anti-resonant element preform is characterized in that the ARE arc element is designed circular and has a radius R_circle, and the ARE arc element is connected to the ARE inner element along a contact line.

The above objectives are also
a cladding tube having a cladding bore and a cladding longitudinal axis along which extends a cladding wall bounded by an inner surface and an outer surface;
- several anti-resonant element preforms;
The anti-resonant element preforms are solved by preforms of anti-resonant hollow-core fibers that are placed in a non-contact, spaced apart relationship to one another at targeted locations on the inner surface of the cladding tube wall.

According to the present invention, it is provided that at least one of the anti-resonant element preforms is designed according to any one of the described embodiments.

Preforms designed in this manner provide easier to produce modal matches and more accurate manufacturing compared to conventional techniques.

All properties and characteristics described with respect to the antiresonant element preform also apply to the preform and vice versa.

The ratio z/R_preform is defined as follows:

Thus, z/R_preform is obtained by dividing the difference between the first segment height H_outer and the second segment height H_inner by the preform core radius R_preform, which thereby identifies the shortest distance between the longitudinal axis of the cladding tube and the anti-resonant element preform.

One embodiment of the preform has a ratio z/R_preform of:
greater than 0.1, in particular greater than 0.2, in particular greater than 0.25;
It is characterised by being smaller than 1, in particular smaller than 0.8, in particular smaller than 0.5.

These parameter spaces for z/R_preform provide good coupling of higher order modes based on adapted phase propagation velocities of the modes in the hollow core fiber produced from the preform. This is especially true for preforms having a length of more than 1 m and an outer diameter of more than 40 mm, in particular more than 90 mm, in particular when the first circle radius R_outer and the second circle radius R_inner of the antiresonant element preform, in addition to the above-mentioned value z/R_preform, are essentially the same length in the preform (R_outer=R_inner).

The term "bore" in reference to cladding does not imply that the bore was produced by a drilling process.

The above mentioned object is also achieved by a method for producing an antiresonant hollow-core fiber preform, comprising:
a) providing a cladding tube having a cladding bore and a cladding longitudinal axis along which a cladding wall extends, the cladding wall being bounded by an inner surface and an outer surface;
b) preparing several anti-resonant element preforms, each including an ARE outer element and an ARE inner element inserted therein;
c) placing the anti-resonant element preform at a target location within the cladding tube bore;
d) subjecting the assembly including the cladding tube and the anti-resonant element preform to a hot forming process selected from at least one of stretching and crushing.

whereby a relative internal pressure in the range of -10 to -300 mbar, in particular -50 to -250 mbar, is established in the cladding bore in step d) "treatment";
The ARE outer element and the ARE inner element are designed in an arc shape in at least one anti-resonant element preform;
It is provided that the ARE outer element and the ARE inner element are connected to each other and to the cladding tube bore along two connecting lines.

Step a)
A cladding tube is prepared as part of step a) "Providing". The cladding tube has a hollow core extending along the cladding tube longitudinal axis. In one embodiment, the cladding tube has an outer diameter in the range of 65-300 mm, preferably 90-250 mm, preferably 120-200 mm. In particular, the cladding tube may have a length of at least 1 m. In one embodiment, the cladding tube comprises or consists of a material transparent to the operating light of the optical fiber, for example glass, in particular doped or undoped quartz glass (SiO2). The doping provides a matching of physical properties, for example the thermal expansion coefficient. Fluorine, chlorine and/or hydroxyl groups are preferably used as doping agents to reduce the viscosity of the quartz glass.

Step b)
Several anti-resonant element preforms are made as part of step b) "preparation". The components or component parts of the preforms that will essentially become anti-resonant elements in the hollow core fiber by simple stretching during the fiber drawing process are referred to as anti-resonant element preforms. The individual anti-resonant element preforms are composed of tubular structural elements, at least some of which may have a wall thickness in the range of 0.1 mm to 2 mm, preferably 0.2 mm to 1.5 mm. The anti-resonant element preforms may be simple components or nested components, with the individual anti-resonant element preforms comprising an outer ARE tube and an inner ARE tube inserted therein. The anti-resonant element preforms have at least two walls with negative curvature (convex) as seen in the direction of the hollow core. By further processing the preforms, in particular by a hot forming step, intermediate products can be made in which the original anti-resonant element preforms are present in a changed shape compared to the original shape.

In one embodiment, the antiresonant element preform comprises or consists of a material transparent to the operating light of the optical fiber, for example glass, in particular doped or undoped quartz glass (SiO2). The doping allows for the adaptation of physical properties, for example the thermal expansion coefficient. Fluorine, chlorine and/or hydroxyl groups are preferably used as doping agents to reduce the viscosity of the quartz glass.

In one embodiment, the anti-resonant element preform and the cladding tube are made of the same material. In a further embodiment, the anti-resonant element preform and the cladding tube are made of the same material, in particular undoped or doped quartz glass (SiO2), with the amount of doping not exceeding 0.1% by weight.

The term "made from the same material" describes the material properties of the two parts, whereby the two parts have essentially the same chemical composition. Thereby, the total mass of different chemical elements in both parts may be less than 1% by weight, in particular less than 0.5% by weight, in particular less than 0.1% by weight. The chemical composition of the two parts differs in particular by a content of contaminants of less than 500 ppm by weight, in particular less than 100 ppm by weight, and/or a content of doping agents of less than 10000 ppm by weight, in particular less than 5000 ppm by weight.

Step c)
As part of step c) "positioning", the anti-resonant element preform is positioned at a target location within the cladding tube bore. After step d) "positioning", the longitudinal axis of the anti-resonant element preform may be aligned essentially parallel to the longitudinal axis of the cladding tube. In an embodiment, the longitudinal axis of the anti-resonant element preform and the longitudinal axis of the cladding tube are designed to be parallel such that the longitudinal axis of the anti-resonant element preform and the longitudinal axis of the cladding tube have an angle of -1.5° to 1.5°, preferably -0.85° to 0.85°, preferably -0.42° to 0.42° with respect to each other. This parallelism ensures that the anti-resonant element preform is placed at the target location within the cladding tube, and therefore that the resonant or anti-resonant conditions, respectively, are respected in the subsequent hollow-core fiber.

Satisfying at least one of the following conditions is essential in order to respect the resonance or anti-resonance conditions, respectively, in the subsequent hollow-core fiber or to further reduce the attenuation in the subsequent hollow-core fiber:
- The anti-resonant element preform must be placed at a pre-calculated target position within the cladding tube.
- The anti-resonant element preform must be placed at a pre-calculated target location within the assembly.
- The anti-resonant element preform must be placed at a pre-calculated target position within the preform.

Step d)
As part of step d) "processing", the assembly comprising the cladding tube, the anti-resonant element preform and the positioning template is further processed by at least one of hot processes of stretching and crushing.

In the context of the present invention, the term stretching is understood to be an increase in the longitudinal expansion of the body. This increase in longitudinal expansion may be associated with a decrease in the lateral expansion of the body. The stretching may be performed to a certain scale, for example, so that the shape and arrangement of the components or components as well as the size ratios (e.g., cladding tube to anti-resonant preform) are reflected in the elongated final product.

In the context of the present invention, the term collapse is understood to mean a reduction in the lateral expansion of the body. Such a reduction in the lateral expansion of the body may occur as part of an increase in the temperature of the body, which may in particular result in an increase in the longitudinal expansion of the body.

The term "hot process" is understood to be a method step in which the temperature of an element is increased by heat input. Examples of hot processes are:
- Flame-based hot processes based on the oxidation of exothermic reaction gases. One example is the use of hydrogen (also called "H2") as combustion gas (flame hydrolysis), which reacts with oxygen, also called "O2", present in the air or supplied externally.
- Flameless high temperature processes use other systems to generate heat and do not require an open flame. One example is the use of resistors to convert electrical energy into thermal energy (heat).

A relative internal pressure in the range of -10 to -300 mbar, in particular -50 to -250 mbar, is set in the cladding bore in step d) "treatment",
The ARE outer element and the ARE inner element are designed in an arc shape in at least one anti-resonant element preform;
It is provided that the ARE outer element and the ARE inner element are connected to each other and to the cladding tube bore along two connecting lines.

The relative internal pressure (negative pressure compared to the ambient atmospheric pressure) in the range of -10 to -300 mbar, especially -50 to -250 mbar, established within the inner bore of the cladding as part of the stretching and/or crushing ensures that the OD/ID ratio (ratio of the cladding outer diameter to the cladding inner diameter) does not become too small.

In the case of antiresonant hollow-core fibers from the prior art, the ARE outer element and the ARE inner element are designed tubular. The nested ARE outer element and the ARE inner element are in each case connected to each other along a connecting line and to the cladding tube. There is therefore a risk that the ARE elements undergo a rotational movement during elongation, thus disturbing the uniformly distributed arrangement of the ARE elements on the inner wall of the cladding tube, which is reflected in an increase in attenuation. This drawback is overcome in the method according to the invention.

One embodiment of the method is characterized in that the ARE outer element has an inner space limited by the ARE outer wall and into which the arc-shaped designed ARE inner element at least partially protrudes. In the case of this embodiment, the risk of deformation of the ARE inner element during crushing and/or stretching is reduced, which in particular leads to variations in the wall thickness of the ARE inner element, which leads to increased attenuation in the subsequent anti-resonant hollow-core fiber.

One embodiment of the method is a method for forming a ARE outer element having a first central angle α_outer and a ARE inner element having a second central angle α_inner, in particular
The first central angle α_outer and/or the second central angle α_inner is characterized by being greater than 310°.

An embodiment of the method is characterized in that in step d) "treatment", the anti-resonant element preform is thermally fixed to the cladding tube wall in a flame-free manner. The position of the anti-resonant element preform in the cladding tube is:
● The anti-resonant element preform may contact the inner surface of the cladding tube bore after step c) "positioning", or ● A gap that is closed during step f) "processing" in particular may still exist between the anti-resonant element preform and the inner surface of the cladding tube bore after step c) "positioning".

In the known method, the anti-resonant element preform is thermally fixed to the cladding tube wall, in particular at the respective ends, via a torch by using a flame. Stretching and/or crushing only takes place afterwards. This has proven to be detrimental to the formation of soot (name for SiO2 particles) and burn-off. These combustion by-products can have different starting points. The combustion of the fuel gas in the torch can be achieved by forming a flame with an excess of combustible material or an excess of oxidants. For example, soot is a known by-product of this type of combustion. Furthermore, the heat input from the torch to the cladding tube can result in local evaporation of the quartz glass. The soot thus produced can then be deposited on individual parts of the preform, in particular on the anti-resonant element preform. This leads to a deterioration in the quality of the final preform, which is manifested in particular by a higher attenuation or broken fibers.

Combustion products or soot deposits form especially on the front surface of the cladding tube, as well as on its inner surface. Moreover, especially the surface of the anti-resonant element preform is affected. Due to the complexity of the geometric shapes produced, a complete cleaning, for example with hydrofluoric acid, is almost impossible. By using a flameless process as part of the "treatment" of step d), the anti-resonant element preform can be connected to the cladding tube wall by a material bond, without soot deposits or combustion in the assembly.

One embodiment of the method is characterized in that the cladding tube has an outer diameter in the range of 65 to 300 mm, preferably 90 to 250 mm, preferably 120 to 200. The cladding tube may in particular have a length of at least 1 m.

The improved accuracy of positioning the anti-resonant element preform within the cladding tube provides anti-resonant element preforms, at least some of which have a wall thickness in the range of 0.2-2 mm, preferably 0.25-1 mm, and cladding tubes having an outer diameter in the range of 65-300 mm, preferably 90-250 mm, preferably 120-200 mm. This further allows each of these components to have a length of at least 1 m.

In one embodiment, the cladding tube comprises or consists of a material transparent to the operating light of the optical fiber, for example glass, in particular doped or undoped quartz glass (SiO2). Doping allows for the adaptation of physical properties, for example the thermal expansion coefficient. Fluorine, chlorine and/or hydroxyl groups are preferably used as doping agents to reduce the viscosity of the quartz glass.

An embodiment of a method for producing a secondary preform from which an anti-resonant hollow-core fiber can be drawn, from a preform produced according to any one of the preceding embodiments, comprising the steps of:
further processing the preform into a secondary preform;
Further processing steps include the following hot forming process:
i.) elongate;
ii.) crushing;
iii.) crush and stretch simultaneously;
Adding additional covering material;
v.) adding additional coating material followed by stretching;
vi.) adding additional coating material and simultaneously stretching;
The present invention includes one or several of the above steps performed once or repeatedly.

A preform, in particular a preform according to the described embodiments, in particular a preform having at least one antiresonant element preform according to the described embodiments, is the starting point for the manufacture of an antiresonant hollow-core fiber. In the method according to the invention, the preform is further processed into a secondary preform by performing one or several hot forming processes.

During stretching, the preform is stretched. The stretching can be performed without simultaneous collapse. The stretching can be performed to a certain scale, for example, so that the shape and arrangement of the components or parts of the preform and the size ratio (e.g., cladding tube to anti-resonant preform) are reflected in the elongated final product of the secondary preform. However, during stretching, the primary preform does not have to be drawn to scale, and its geometry can be changed. During collapse, the inner bore is narrowed or the ring gap between the tubular components is closed or narrowed. The collapse can be associated with the stretching. The secondary preform produced in this way can already be designed and suitable for drawing a hollow-core fiber. The secondary preform can be optionally further processed, for example, elongated or additional cladding material is added.

One embodiment of the method is characterized in that at least one of the anti-resonant element preforms is designed according to any one of the preceding embodiments.

All of the properties and characteristics described with respect to the antiresonant element preform also apply to this method and vice versa.

The above mentioned object is also solved by an anti-resonant hollow-core fiber,
a coating having an inner coating bore and a coating longitudinal axis along which a coating wall extends, the coating wall being bounded by an inner coating surface and an outer coating surface;
several anti-resonant elements, each comprising an ARE outer unit and an ARE inner unit, the ARE outer unit designed in an arc shape and the ARE inner unit being connected to each other along two seam lines;
The anti-resonant elements are placed at targeted positions on the cladding inner surface of the cladding wall, spaced apart from each other and in a non-contact manner.

According to the present invention, the ARE outer unit is provided with an inner space that is at least partially bounded by the ARE outer wall and into which the ARE inner unit, designed in an arc shape, at least partially protrudes.

In order to provide a single-mode wave in the core of the anti-resonant hollow-core fiber, it is necessary to attenuate the higher-order modes that are coupled in the same way. If possible, this is done within the first few meters of the optical anti-resonant hollow-core fiber. In the case of NANF fibers, the anti-resonant elements serve to attenuate these higher-order modes. Thereby, one aspect is the geometrical design of the ARE-inner and ARE-outer units, both alone and mutually. The mutual matching of the ARE-inner and ARE-outer units with the aim of attenuating the higher-order modes is also called mode matching. Compared to anti-resonant hollow-core fibers from the prior art, the anti-resonant hollow-core fiber according to the invention:
The ARE outer unit and the ARE inner unit have negative curvature, which has a positive effect on damping;
- Options according to the present invention allow the use of virtually any combination for the radii of the ARE-inner and ARE-outer units.

This degree of freedom provides improved mode matching in antiresonant hollow-core fibers.

In one embodiment, at least one seam line and the coating longitudinal axis are designed to be parallel, and thus, in particular, both the seam line and the coating longitudinal axis have an angle of -1.5 degrees to 1.5 degrees, preferably -0.85 degrees to 0.85 degrees, preferably -0.42 degrees to 0.42 degrees, with respect to each other. This parallelism ensures an improved mode match in the anti-resonant hollow-core fiber.

An embodiment of the anti-resonant hollow-core fiber is characterized in that the anti-resonant hollow-core fiber has three, four, five, six, seven or eight anti-resonant elements, and in particular, the anti-resonant hollow-core fiber has an odd number of anti-resonant elements. This number has proven to be particularly advantageous in reducing attenuation in the anti-resonant hollow-core fiber.

One embodiment of an anti-resonant hollow-core fiber is characterized in that the anti-resonant hollow-core fiber has the following features:
The anti-resonant elements are arranged symmetrically on the inner surface of the cladding wall.
at least one of the ARE outer unit and/or the ARE inner unit is made of an amorphous solid, in particular of glass, in particular of quartz glass, in particular of glass having a refractive index of at least 1.4, in particular from 1.4 to 3, in particular from 1.4 to 2.8;
the wall thickness of the ARE outer unit and the ARE inner unit are essentially the same.

The term "essentially the same wall thickness" should be understood such that under practical conditions and manufacturing techniques, mathematically exactly the same wall thickness cannot be achieved, but can only be provided within certain manufacturing-related error tolerances. The term "essentially the same wall thickness" is therefore understood to be a difference in wall thickness between the ARE outer unit and the ARE inner unit of less than 5%, in particular less than 2.5%, in particular less than 1.5%.

One embodiment of an anti-resonant hollow-core fiber is characterized in that the anti-resonant hollow-core fiber has the following features:
● Basic attenuation of less than 0.15 dB/km at transmission wavelengths of 1.0 to 2.5 μm;
- a fundamental attenuation of less than 1 dB/km at transmission wavelengths up to 0.8 μm.

An embodiment of the anti-resonant hollow core fiber is characterized in that the anti-resonant element forms a core having a core radius smaller than 50 μm, in particular smaller than 40 μm, in particular smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 20 μm, in particular smaller than 15 μm, in particular smaller than 13 μm. The core radius is therefore the shortest distance between the longitudinal axis of the anti-resonant hollow core fiber and the ARE outer unit.

The anti-resonant hollow-core fiber has a Bolt circle radius that is the sum of the core radius and a third circle radius FB_outer. An embodiment of the anti-resonant hollow-core fiber is characterized by a Bolt circle radius smaller than 40 μm, in particular smaller than 38 μm, in particular smaller than 33 μm. An embodiment of the anti-resonant hollow-core fiber is characterized by a Bolt circle radius larger than 20 μm, in particular larger than 25 μm, in particular larger than 29.5 μm.

One embodiment of an anti-resonant hollow-core fiber is characterized in that the anti-resonant hollow-core fiber has the following features:
The ARE outer unit has a third circle radius FB_outer;
The ARE inner unit has a fourth circle radius FB_inner;
The ARE outer unit has a third central angle β_outer;
The ARE inner unit is characterized by having at least one of the following: having a fourth central angle β_inner.

One embodiment of an anti-resonant hollow-core fiber comprises:
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 15 μm;
FB_outer is greater than 5 μm, in particular greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 15 μm;
FB_inner is characterized in having at least one of the following: greater than 5 μm, in particular greater than 10 μm, in particular greater than 12 μm.

An anti-resonant hollow core fiber embodiment of this type has lower attenuation. Optimized mode matching can be performed with the degrees of freedom gained in accordance with the present invention.

The term "essentially the same length" should be understood such that under practical conditions and manufacturing techniques, mathematically exactly the same length cannot be achieved, but is only possible within certain manufacturing-related error tolerances. In this respect, the term "essentially the same length" is understood to mean that the amount of deviation of the third circle radius FB_outer from the fourth circle radius is less than 5%, in particular less than 3%, in particular less than 2%, in particular less than 1.5%, in particular less than 1% of the third circle radius FB_outer.

One embodiment of an anti-resonant hollow-core fiber comprises:
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 25 μm, in particular smaller than 22 μm, in particular smaller than 20 μm, in particular smaller than 17 μm, in particular smaller than 16 μm;
FB_outer is greater than 5 μm, in particular greater than 7 μm, in particular greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 25 μm, in particular smaller than 22 μm, in particular smaller than 20 μm, in particular smaller than 17 μm, in particular smaller than 16 μm;
FB_inner is characterized in having at least one of the following: greater than 5 μm, in particular greater than 7 μm, in particular greater than 10 μm, in particular greater than 12 μm.

One embodiment of an anti-resonant hollow-core fiber comprises:
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
Anti-resonant elements have the following characteristics:
FB_outer is 16.5 μm or less, particularly 15.75 μm or less;
FB_outer is 11.5 μm or more, particularly 12.25 μm or more;
FB_inner is 16.5 μm or less, particularly 15.75 or less;
FB_inner is 11.5 μm or more, in particular 12.25 μm or more.

Anti-resonant hollow-core fiber embodiments of this type have low attenuation.

One embodiment of an anti-resonant hollow-core fiber comprises:
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
At least one anti-resonant element has the following characteristics:
β_outer is smaller than 350°, in particular smaller than 345°, in particular smaller than 340°;
β_outer is greater than 275°, in particular greater than 295°, in particular greater than 320°,
β_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
- β_inner is characterized in having at least one of the following: greater than 30°, in particular greater than 40°, in particular greater than 50°.

One embodiment of the anti-resonant hollow-core fiber has a fundamental mode confinement loss of less than 10E-2 db/m;
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner), and the amount of deviation of the third circle radius FB_outer from the fourth circle radius is less than 2% of the third circle radius FB_outer;
The anti-resonant hollow-core fiber has five, six, or seven anti-resonant elements;
Anti-resonant elements have the following characteristics:
The bow ratio is greater than 1.6 and less than 3.0.
FB_outer and FB_inner are equal to or less than 16.5 μm, in particular equal to or less than 15.75 μm;
FB_outer and FB_inner are 11.5 μm or more, particularly 12.25 μm or more.

This embodiment of the antiresonant hollow-core fiber in particular has a fundamental mode confinement loss (also called waveguide loss) of less than 10E-2 db/m (and thus 0.01 db/m), which is highly advantageous.

Hollow-core fibers are generally multimode waveguides. In addition to the fundamental mode, the core also guides higher-order modes (hereinafter also referred to as "higher-order modes" or "HOMs"). HOMs have higher waveguide losses than the fundamental mode. In this respect, hollow-core fibers behave pseudo-to the fundamental mode after a longer travel distance. However, it is advantageous if this travel distance is as short as possible.

To improve the fundamental mode behavior of the fiber, an additional loss mechanism can be used, where the energy of the HOMs is coupled into high-loss modes in the ARE unit (ARE outer unit and/or ARE inner unit) by a tailored design of the hollow-core fiber. This coupling can occur in two groups of modes:
It requires adapted transport propagation velocities of the ARE modes in the ARE units (ARE-outer unit and/or ARE-inner unit) and the HOMs in the core of the hollow-core fiber.

Good coupling of the phase propagation velocities of the two mode groups exists when the effective modal index n _eff of both mode groups essentially corresponds.

The coupling of phase propagation velocities can be influenced, inter alia, by the geometry of the individual components of the hollow-core fiber. In particular, the parameter "z/R" turns out to be important, which is defined as:

In this respect, z/R is obtained from the difference between the third segment height HF_outer (see 2424 in FIG. 20) and the fourth segment height HF_inner (see 2434 in FIG. 20) divided by the core radius R_fiber (see 2405 in FIG. 20). In an alternative embodiment of a hollow-core fiber, z/R is given by:
greater than 0.6, especially greater than 0.7, especially greater than 0.8,
● Less than 1.4, especially less than 1.3, especially less than 1.2.

In particular, z/R is in the interval [0.8;1.2]. This parameter space for z/R provides a good coupling of the phase propagation velocities of the two modes.

To achieve low confinement loss of the fundamental mode, particularly less than 10E-2 db/m, as well as fundamental mode behavior over short fiber distances, one embodiment of an anti-resonant hollow-core fiber has a ratio z/R of:
- greater than 0.75, especially greater than 0.8,
● Less than 1.25, especially less than 1.2,
The third circle radius FB_outer and the fourth circle radius FB_inner can be characterized as being essentially the same length (FB_outer = FB_inner), FB_outer and FB_inner being smaller than 17 μm and greater than 12 μm, and the bow ratio being smaller than 2.8 and greater than 1.6.

One embodiment of an anti-resonant hollow-core fiber comprises:
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
The wall thickness of the ARE-outer unit and/or the ARE-inner unit is characterized in that at a signal wavelength of 1550 nm in the first transmission window, it is between 0.35 μm and 0.65 μm, in particular between 0.4 μm and 0.6 μm, in particular 0.5 μm.

One embodiment of an anti-resonant hollow-core fiber comprises:
the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner);
The wall thickness of the ARE-outer unit and/or the ARE-inner unit is characterized in that at a signal wavelength of 1550 nm in the second transmission window it is between 1.25 μm and 0.75 μm, in particular between 1.1 μm and 0.9 μm, in particular 1 μm.

One embodiment of an anti-resonant hollow-core fiber comprises:
The third circle radius FB_outer is longer than the fourth circle radius FB_inner (FB_outer>FB_inner),
At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 15 μm;
FB_outer is greater than 5 μm, in particular greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 20 μm, in particular smaller than 15 μm, in particular smaller than 11 μm;
FB_inner is characterized in having at least one of the following: greater than 2 μm, in particular greater than 4 μm, in particular greater than 6 μm.

The option of having the fourth circle radius FB_inner of the ARE inner unit larger than the third circle radius FB_outer of the ARE outer unit allows for improved mode matching.

One embodiment of an anti-resonant hollow-core fiber comprises:
The third circle radius FB_outer is longer than the fourth circle radius FB_inner (FB_outer>FB_inner),
At least one anti-resonant element has the following characteristics:
β_outer is smaller than 350°, in particular smaller than 345°, in particular smaller than 340°;
β_outer is greater than 275°, in particular greater than 295°, in particular greater than 320°,
β_inner is smaller than 300°, in particular smaller than 285°, in particular smaller than 230°,
- β_inner is characterized in having at least one of the following: greater than 100°, in particular greater than 120°, in particular greater than 150°.

One embodiment of an anti-resonant hollow-core fiber comprises:
The third circle radius FB_outer is shorter than the fourth circle radius FB_inner (FB_outer<FB_inner),
At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 30 μm, in particular smaller than 25 μm, in particular smaller than 15 μm;
FB_outer is greater than 5 μm, in particular greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 20 μm, in particular smaller than 15 μm, in particular smaller than 11 μm;
FB_inner is characterized in having at least one of the following: greater than 2 μm, in particular greater than 4 μm, in particular greater than 6 μm.

This type of anti-resonant hollow core fiber design has low attenuation.

One embodiment of an anti-resonant hollow-core fiber comprises:
The third circle radius FB_outer is shorter than the fourth circle radius FB_inner (FB_outer<FB_inner),
At least one anti-resonant element has the following characteristics:
β_outer is smaller than 340°, in particular smaller than 315°, in particular smaller than 305°;
β_outer is greater than 200°, in particular greater than 220°, in particular greater than 250°,
β_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°,
- β_inner is characterized in having at least one of the following: greater than 30°, in particular greater than 40°, in particular greater than 50°.

One embodiment of the anti-resonant hollow-core fiber is characterized in that the third central angle β_outer and/or the fourth central angle β_inner is smaller than 350°, in particular the third central angle β_outer and/or the fourth central angle β_inner is [200°; 340°], in particular [250°; 330°], in particular [300°; 320°].

One embodiment of the anti-resonant hollow-core fiber is characterized in that the ARE outer unit has a third segment height HF_outer and the ARE inner element has a fourth segment height H_inner, in particular
The ratio of the third segment height HF_outer to the fourth segment height is less than 30 (HF_outer/HF_inner<30).

The third segment height HF_outer refers to the distance from the apex of the ARE outer unit to the string. The fourth segment height HF_inner refers to the distance from the apex of the ARE inner unit to the string. By appropriately selecting the ratio, the attenuation of the anti-resonant hollow-core fiber can be made low.

This embodiment further includes at least one anti-resonant element having the following features:
HF_outer/HF_inner is less than 6.5, especially less than 4, especially less than 3.2;
It may be further modified to the effect that HF_outer/HF_inner is at least one of: greater than 1.7, in particular greater than 1.75, in particular greater than 1.85.

This embodiment is particularly advantageous in the case of an anti-resonant hollow-core fiber, where the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer = FB_inner).

One embodiment of the anti-resonant hollow-core fiber is characterized in that the ARE-arc unit is disposed within the ARE-outer unit. To provide a single-mode wave in the core, higher order modes must be attenuated within the anti-resonant hollow-core fiber. To achieve this goal, the ARE-outer unit can be complemented by an ARE-arc unit.

An embodiment of the anti-resonant hollow core fiber is characterized in that the ARE arc unit is designed in a circular arc shape, has a sixth circular radius FB_arc and a sixth central angle β_arc, and the ARE arc unit is connected to the ARE outer unit and/or the ARE inner unit along two contact seams.

One embodiment of the anti-resonant hollow core fiber is characterized in that the ARE arc unit is designed circular and has a radius FB_circle, and the ARE arc unit is connected to the ARE inner unit along a contact seam.

As part of the stretching and/or collapsing, ARE arc units can be created from ARE arc elements. Therefore, in terms of design, the statements made regarding ARE arc elements also apply to ARE arc units.

One embodiment of the anti-resonant hollow core fiber is characterized in that the fundamental attenuation difference between a straight anti-resonant hollow core fiber and an anti-resonant hollow core fiber wound to a diameter of 10 mm is two orders of magnitude smaller, in particular an order of magnitude smaller, in particular less than half an order of magnitude.

One embodiment of the anti-resonant hollow core fiber is characterized in that it is manufactured from a preform described in any one of the preceding embodiments.

All properties and characteristics described for the preform also apply to the anti-resonant hollow-core fiber and vice versa.

One embodiment of the anti-resonant hollow core fiber is characterized in that it is manufactured using a method as described in any one of the preceding embodiments.

All of the properties and characteristics described for the anti-resonant hollow-core fiber also apply to the preform and/or anti-resonant hollow-core fiber and/or method, and vice versa.

The above object is also achieved by a method for producing an anti-resonant hollow-core fiber from a preform produced according to any one of the preceding embodiments, in particular produced using a method according to any one of the preceding embodiments, comprising:
further processing the preform into an anti-resonant hollow-core fiber;
Further processing steps include the following hot forming process:
i.) elongate;
ii.) crushing;
iii.) crush and stretch simultaneously;
iv.) adding additional coating material;
v.) adding additional coating material followed by stretching;
vi.) adding additional coating material and simultaneously stretching;
The present invention includes one or several of the above steps performed once or repeatedly.

For further processing to produce an anti-resonant hollow-core fiber from the preform, the preform can be guided vertically through a furnace, whereby the lower end of the preform, from which the anti-resonant hollow-core fiber is drawn in the form of a cone, is warmed to the drawing temperature, and the drawn anti-resonant hollow-core fiber is then cooled from the drawing temperature by a gas flow directed against the drawing direction.

In one embodiment, the anti-resonant hollow core fiber is coated with a protective layer, a step that is performed during the drawing process in the course of glass fiber manufacturing. The plastic used for the coating can be one or several of the following materials: polyurethane acrylate, acrylate, polyolefin, polyamide (nylon), polyether, polyurethane monoacrylate, fluoroalkyl methacrylate, or polyimide.

One embodiment of a method for producing an anti-resonant hollow-core fiber is characterized in that a relative internal pressure in the range of 0.05 mbar to 20 mbar is established in the core region during a "further processing" step as part of stretching the preform into an anti-resonant hollow-core fiber.

If the relative internal pressure is less than 0.05 mbar, the anti-resonant hollow-core fiber may be crushed too much. Conversely, if the relative internal pressure in the core region is greater than 20 mbar, the anti-resonant hollow-core fiber may expand too strongly.

The temperature of the heating zone during the hot forming process should be as constant as possible. Advantageously, temperature-controlled heating elements whose target temperature is held to exactly +/- 0.1° are used during the hot forming process. Thus, the temperature fluctuations in the hot forming process can be limited to less than +/- 0.5°C.

In particular, at least one of the following transitions may occur during the production of an anti-resonant hollow-core fiber from a preform according to any one of the preceding embodiments, in particular during the “further processing” steps:
The anti-resonant element is generated from an anti-resonant element preform,
At least a portion of the coating is generated from a cladding tube;
The ARE Outside Unit is created from the ARE Outside Elements.
ARE-inner units are created from ARE-inner elements,
A third circle radius FB_outer is created from the first circle radius R_outer;
The fourth circle radius FB_inner is generated from the second circle radius R_inner;
A third central angle β_outer is created from the first central angle α_outer,
The fourth central angle β_inner is generated from the second central angle α_inner;
A third segment height HF_outer is generated from the first segment height H_outer;
A fourth segment height HF_inner is generated from the second segment height H_inner;
●Seam lines are generated from connection lines,
ARE arc units are generated from ARE arc elements.
The sixth circle radius FB_arc is generated from the fifth circle radius R_arc;
The radius FB_circle is generated from the radius R_circle.
The sixth central angle β_arc is generated from the fifth central angle α_arc;
●The contact seam is formed from a contact line and can be part of.

Thus, all of the properties and characteristics described for the antiresonant element preform also apply to the preform and/or antiresonant hollow core fiber and/or method, and vice versa.

The properties and features disclosed herein may be important both separately and in combination with one another to the various embodiments of the invention as claimed. Properties and features disclosed with respect to the antiresonant element preform, or the preform, or the antiresonant hollow-core fiber are also disclosed with respect to the method, and vice versa.

The present invention will now be described in further illustrative terms with reference to the drawings. The present invention is not limited to the drawings.

FIG. 1 shows the ARE outer element designed in an arc shape. FIG. 2 shows an ARE inner element designed in an arc shape. FIG. 3 shows the anti-resonant element preform along with a close-up cross-sectional view of the connecting lines. FIG. 4 illustrates a further embodiment of an anti-resonant element preform. FIG. 5 illustrates a further embodiment of an anti-resonant element preform. FIG. 6 illustrates a further embodiment of an anti-resonant element preform. FIG. 7 illustrates a further embodiment of an anti-resonant element preform. FIG. 8 illustrates a further embodiment of an anti-resonant element preform. FIG. 9 illustrates a further embodiment of an anti-resonant element preform. FIG. 10 illustrates a further embodiment of an anti-resonant element preform. FIG. 11 illustrates a further embodiment of an anti-resonant element preform. FIG. 12 illustrates a further embodiment of an anti-resonant element preform. FIG. 13 illustrates a further embodiment of an anti-resonant element preform. FIG. 14 illustrates a further embodiment of an anti-resonant element preform. FIG. 15 illustrates a further embodiment of an anti-resonant element preform. FIG. 16 shows a cross-sectional view of a preform for producing an anti-resonant hollow-core fiber. FIG. 17 illustrates a further embodiment of an anti-resonant element preform. FIG. 18 illustrates a further embodiment of an anti-resonant element preform. FIG. 19 shows a partial longitudinal cross-section of an anti-resonant hollow-core fiber. FIG. 20 shows a cross-sectional view of an anti-resonant hollow-core fiber according to FIG. FIG. 21 shows a longitudinal cross section of the cladding tube. FIG. 22 shows a longitudinal section of an element of a further embodiment of a preform. FIG. 23 shows a longitudinal section of a preform having the elements of FIG. FIG. 24 shows a longitudinal section of an element of a further embodiment of a preform. FIG. 25 shows a longitudinal section of a preform having the elements of FIG. FIG. 26 shows the extension of the assembly into a preform. FIG. 27 shows method steps for manufacturing a preform. FIG. 28 illustrates method steps for fabricating an anti-resonant hollow-core fiber. FIG. 29 shows a diagram with the confinement loss of the fundamental mode plotted over the Bow ratio. FIG. 30 shows a diagram with the effective mode index plotted against the ratio z/R.

Figure 1 shows a cross section through the ARE outer element 310. The ARE outer element 310 is a tubular structure having an arc-shaped cross section. The ARE outer element 310 extends along a first longitudinal axis 311. Thus, in Figure 1, the ARE outer element 310 extends in the plane of the drawing.

The ARE outer element 310 has an ARE outer wall 315 made of or made of a material that is transparent to the operating light of the optical fiber, e.g. glass, in particular doped or undoped quartz glass (SiO2). In one embodiment, the ARE outer wall 315 has a wall thickness in the range of 0.1 mm to 2 mm, preferably 0.2 mm to 1.5 mm. In one embodiment, the ARE outer element 310 has a length of at least 1 m, in particular a length of 0.2 to 10 m, in particular a length of 1 to 5 m.

The cross section shown in FIG. 1 makes it clear that the ARE outer element 310 has an arc-shaped cross section. In the context of the present invention, the term "arc" is understood to be a portion of a circumference. Two points on a circle divide the circumference into two arcs. In the framework of the present invention, an element is described as "arc-shaped" if its contour follows the path of one of the two arcs.

For clarity, a first circle 298 is depicted in FIG. 1. This first circle 298 is divided into two arcs by two cut lines Q-Q and R-R. The cross section of the ARE outer element 310 follows one of the two arcs.

A cutting line P-P is further drawn through two intersections of the two cutting lines Q-Q and R-R with the first circle 298. The distance on the cutting line P-P and bounded by the cutting lines Q-Q and R-R is called the first chord of the ARE outer element 310. The length of the first chord is referred to as the first chord length.

The ARE outer element 310 has a first circle radius R_outer 320. This first circle radius R_outer 320 represents the distance from the ARE outer wall 315 to the first longitudinal axis 311.

The ARE outer element 310 has a first segment height 328. This first segment height 328 represents the length of a straight line perpendicular to the first chord and extending to the apex of the ARE outer wall 315.

The ARE outer element 310 has a first central angle α_outer 325. This first central angle α_outer 325 represents the angle at which its apex is located at the center of the first circle 298 and its arms intersect with the limits of the arc (here, the intersections of the first circle 298 with the cutting lines Q-Q and R-R). A complete circle has a degree of 360°. Due to the ARE outer element 310 being formed in an arc, the first central angle α_outer 325 is less than 360°.

The ARE outer element 310 has an inner space 317 bounded by the ARE outer wall 315 and the first chord.

Figure 2 shows a cross-section of the ARE inner element 340. The ARE inner element 340 is a tubular structure having an arc-shaped cross-section. The ARE inner element 340 extends along a second longitudinal axis 341. Thus, in Figure 2, the ARE inner element 340 extends in the plane of the drawing.

The ARE inner element 340 has a wall 345 that includes or consists of a material transparent to the operating light of the optical fiber, for example glass, in particular doped or undoped quartz glass (SiO2). In one embodiment, the wall 345 has a wall thickness in the range of 0.1 mm to 2 mm, preferably 0.2 mm to 1.5 mm. In one embodiment, the ARE outer element 310 has a length of at least 1 m, in particular a length of 0.2 to 10 m, in particular a length of 1 to 5 m.

The ARE inner element 340 has a cross section that is an arc. For clarity, a second circle 299 is drawn in FIG. 2. This second circle 299 is divided into two arcs by two cut lines H-H and I-I. The cross section of the ARE inner element 340 follows one of the two arcs.

Furthermore, a cut line G-G is drawn through two intersections of the two cut lines H-H and I-I with the second circle 299. The distance on the cut line G-G and bounded by the cut lines H-H and I-I is called the second chord of the ARE inner element 340. The length of the second chord is called the second chord length.

The ARE inner element 340 has a second segment height 358. This second segment height 358 represents the length of a straight line perpendicular to the second chord and extending to the apex of the wall 345.

Additionally, the ARE inner element 340 has a second circle radius R_inner 350. This second circle radius R_inner 350 represents the distance from the wall 345 to the second longitudinal axis 341.

The ARE inner element 340 has a second central angle α_inner 355. This second central angle α_inner 355 represents the angle at which its vertex is at the center of the second circle 299 and its sides intersect with the boundary points of the arc (here, the intersections of the second circle 299 with the cutting lines H-H and I-I). A complete circle has a degree of 360°. Because the ARE inner element 340 is formed in an arc shape, the second central angle α_inner 355 is less than 360°.

The ARE inner element 340 has an inner space 347 bounded by a wall 345 and a second chord.

1 and 2 show cross-sections and therefore axial top views on the ARE outer element 310 and the ARE inner element 340. In the illustrated two-dimensional views relative to their respective longitudinal axes 311 and 341, the ARE outer element 310 and the ARE inner element 340 have arc-shaped cross-sections that correspond to tubular structural elements in the three-dimensional views.

The respective arcs of the ARE outer element 310 and/or the ARE inner element 340 are designed to be essentially circular, in particular such that the first circle radius R_outer 320 and/or the second circle radius R_inner 350 at a first point do not deviate from the first circle radius R_outer 320 and/or the second circle radius R_inner 350 at a further point by more than 5%, preferably by more than 3%, more preferably by more than 1%, most preferably by more than 0.5%.

In the context of the present invention, a statement that two lengths, e.g. a first circle radius R_outer 320 and a second circle radius R_inner 350, are the same length is understood to mean that the lengths are the same within manufacturing related tolerances, in particular that the lengths differ by less than 1.5%, in particular less than 1.0%, in particular less than 0.5%.

Figure 3 shows an anti-resonant element preform 300 having an ARE outer element 310 designed in an arc shape and an ARE inner element 340 designed in an arc shape, as shown in Figures 1 and 2.

The arc-shaped ARE outer element 310 and the arc-shaped ARE inner element 340 are connected to each other along two connecting lines 370, 370' arranged essentially parallel to the first longitudinal axis 311. This connection can be carried out in particular by a high-temperature process.

For clarity, a portion of the anti-resonant element preform 300 is shown in expanded form around a connecting line 370 in FIG.
a first end point of the ARE outer wall 315 of the ARE outer element 310, continuing from the intersection of the first circle 298 with the cutting lines Q-Q and R-R;
• Occurs between the second end point of wall 345 of ARE inner element 340 continuing from the intersection of second circle 299 with cutting lines HH and II.

Due to the fact that a cross section is shown in FIG. 3, the two connection lines 370, 370' in the three-dimensional anti-resonant element preform 300 extend in the plane of the drawing.

1, the ARE outer element 310 has an inner space 317 at least partially limited by the ARE outer wall 315. Similarly, the ARE inner element 340 has an inner space 347 at least partially limited by the wall 345 shown in FIG. 2. The ARE inner element 340, designed in an arc, at least partially projects into the inner space 317. In the context of the present invention, this is understood in such a way that, in cross section, the ARE inner element 340 essentially extends above the first chord of the ARE outer element 310. In particular, deviations from this positioning of the ARE inner element 340 are limited by the expansion associated with the manufacture of the two connecting lines 370, 370' that may project from the inner space 317. In cross section, in particular not more than 5%, in particular not more than 2.5%, in particular not more than 1% of the second central angle α_inner 355 of the ARE inner element 340 may project from the inner space 317.

The anti-resonant element preform 300 shown in Figure 3 can be manufactured separately from the further components for producing an anti-resonant hollow-core fiber. Thus, the accuracy of the anti-resonant element preform 300 can be inspected before installation in the preform to ensure that only defect-free anti-resonant element preforms 300 are used. In accordance with the present invention, the illustrated anti-resonant element preform 300:
the ARE outer element 310 and the ARE inner element 340 of the anti-resonant hollow-core fiber have a negative curvature that positively affects the attenuation;
- Characterized by the fact that, depending on the options according to the present invention, virtually any combination of radii of the ARE inner element 340 and the ARE outer element 310 can be used.

Figures 4 to 15 show various embodiments of the anti-resonant element preform. The embodiments according to Figures 4 and 15 correspond largely to the embodiments described above and shown in Figures 1 and 3, and therefore reference is made to the above description to avoid repetition. Structures repeated from the description of Figures 1 to 3 bear the same reference numbers. Modifications of the structure compared to the structure shown in Figures 1 to 3 bear the same reference numbers with an additional letter.

Figures 4-8 show further embodiments of anti-resonant element preforms in which the first circular radius R_outer of the ARE outer element is greater than the second circular radius R_inner of the ARE inner element.

FIG. 4 illustrates one embodiment of an anti-resonant element preform 300a where a first circular radius R_outer 320a of an ARE outer element 310a is greater than a second circular radius R_inner 350a of an ARE inner element 340a;
The first circle radius R_outer 320a is greater than 2 mm and less than 10 mm;
The second circle radius R_inner 350a is greater than 1 mm and less than 6 mm;
The first central angle α_outer is greater than 295° and less than 350°;
The second central angle α_inner is greater than 210° and less than 260°.

The anti-resonant element preform 300a designed in this manner has the following features:
the second longitudinal axis 341a is above the first chord;
- first longitudinal axis 311a passes through the exterior of ARE inner element 340a;
The angle between the ARE outer wall 315 and the wall 345 is obtuse, in particular within [60°; 130°], in particular within [70°; 120°];
The ratio of the first segment height to the second segment height may be between 3 and 6.

FIG. 5 illustrates one embodiment of an anti-resonant element preform 300b where a first circular radius R_outer 320b of an ARE outer element 310b is greater than a second circular radius R_inner 350b of an ARE inner element 340b;
The first circle radius R_outer is greater than 1 mm and less than 11 mm;
The second circle radius R_inner is greater than 5 mm and less than 9 mm;
The first central angle α_outer is greater than 315° and less than 350°;
The second central angle α_inner is greater than 280° and less than 315°.

The anti-resonant element preform 300b designed in this manner has the following features:
the second longitudinal axis 341b is above the first chord;
First longitudinal axis 311b passes through the interior of ARE inner element 340b;
The angle between the ARE outer wall 315 and the wall 345 is within [5°; 40°], in particular within [10°; 30°];
The ratio of the first segment height to the second segment height may be between 1 and 3.

6 illustrates one embodiment of an anti-resonant element preform 300c where a first circular radius R_outer 320c of an ARE outer element 310c is greater than a second circular radius R_inner 350c of an ARE inner element 340c. Some of the geometric values are similar to those from FIG. 5:
The first circle radius R_outer is greater than 2 mm and less than 10 mm;
The second circle radius R_inner is greater than 5 mm and less than 9 mm;
The first central angle α_outer is greater than 315° and smaller than 350°.

However, now only a small portion of the ARE inner element 340c is located inside the ARE outer element 310c,
The second central angle α_inner is greater than 49° and less than 65°.

The anti-resonant element preform 300c designed in this manner has the following features:
the second longitudinal axis 341c is above the first chord;
- first longitudinal axis 311c passes through the exterior of ARE inner element 340c;
the angle between the ARE outer wall 315 and the wall 345 is within [120°; 170°], in particular within [130°; 150°];
The ratio of the first segment height to the second segment height may be between 20 and 30.

FIG. 7 illustrates one embodiment of an anti-resonant element preform 300d where a first circular radius R_outer 320d of an ARE outer element 310d is greater than a second circular radius R_inner 350d of an ARE inner element 340d;
The first circle radius R_outer is greater than 2 mm and less than 10 mm;
The second circle radius R_inner is greater than 7 mm and less than 12 mm;
The first central angle α_outer is greater than 270° and less than 310°;
The second central angle α_inner is greater than 200° and less than 250°.

The anti-resonant element preform 300d designed in this manner has the following features:
the second longitudinal axis 341d is above the first chord;
First longitudinal axis 311d passes through the exterior of ARE inner element 340d;
The angle between the ARE outer wall 315 and the wall 345 is within [35°; 100°], in particular within [45°; 90°];
The ratio of the first segment height to the second segment height may be between 1 and 3.

8 illustrates one embodiment of an anti-resonant element preform 300e where a first circular radius R_outer 320e of an ARE outer element 310e is greater than a second circular radius R_inner 350e of an ARE inner element 340e. Thus, some of the geometric values are similar to those from FIG.
The first circle radius R_outer is smaller than 10 mm and larger than 2 mm;
The second circle radius R_inner is smaller than 12 mm and larger than 7 mm;
The first central angle α_outer is smaller than 310° and greater than 270°.

However, now only a small portion of the ARE inner element 340e is located inside the ARE outer element 310e,
The second central angle α_inner is greater than 120° and less than 150°.

The anti-resonant element preform 300e designed in this manner has the following features:
the second longitudinal axis 341e is below the first chord;
First longitudinal axis 311e passes through the exterior of ARE inner element 340e;
The angle between the ARE outer wall 315 and the wall 345 is within [35°; 100°], in particular within [45°; 90°];
• the ratio of the first segment height to the second segment height is between 1 and 6.

Figures 9-13 show various embodiments of anti-resonant element preforms in which the first circular radius R_outer of the ARE outer element is smaller than the second circular radius R_inner of the ARE inner element.

FIG. 9 illustrates one embodiment of an anti-resonant element preform 300f where a first circular radius R_outer 320f of an ARE outer element 310f is less than a second circular radius R_inner 350f of an ARE inner element 340f;
The first circle radius R_outer is greater than 2 mm and less than 10 mm;
The second circle radius R_inner is greater than 1 mm and less than 9 mm;
The first central angle α_outer is greater than 270° and less than 330°;
The second central angle α_inner is greater than 30° and less than 70°.

The anti-resonant element preform 300f designed in this manner has the following features:
the second longitudinal axis 341 is below the first chord;
first longitudinal axis 311f passes through the exterior of ARE inner element 340f;
The angle between the ARE outer wall 315 and the wall 345 is within [35°; 100°], in particular within [45°; 90°];
The ratio of the first segment height to the second segment height may be between 13 and 19.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 9.

FIG. 10 illustrates one embodiment of an anti-resonant element preform 300g where a first circular radius R_outer 320g of an ARE outer element 310g is less than a second circular radius R_inner 350g of an ARE inner element 340g;
The first circle radius R_outer is greater than 2 mm and less than 10 mm;
The second circle radius R_inner is greater than 1 mm and less than 9 mm;
The first central angle α_outer is greater than 210° and less than 250°;
The second central angle α_inner is greater than 90° and less than 115°.

The anti-resonant element preform 300g designed in this manner has the following characteristics:
the second longitudinal axis 341 is below the first chord;
First longitudinal axis 311g passes through the exterior of ARE inner element 340g;
The angle between the ARE outer wall 315 and the wall 345 is within [30°; 90°], in particular within [45°; 85°];
• the ratio of the first segment height to the second segment height is between 1 and 6.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 10.

FIG. 11 illustrates one embodiment of an anti-resonant element preform 300h, where a first circular radius R_outer 320h of an ARE outer element 310h is less than a second circular radius R_inner 350h of an ARE inner element 340h;
The first circle radius R_outer is greater than 2 mm and less than 10 mm;
The second circle radius R_inner is greater than 20 mm and less than 30 mm;
The first central angle α_outer is greater than 270° and less than 330°;
The second central angle α_inner is greater than 15° and less than 45°.

The anti-resonant element preform 300h designed in this manner has the following features:
the second longitudinal axis 341 is below the first chord;
- first longitudinal axis 311h passes through the exterior of ARE inner element 340h;
The angle between the ARE outer wall 315 and the wall 345 is within [70°; 110°], in particular within [80°; 100°];
• the ratio of the first segment height to the second segment height is between 17 and 35.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 11.

FIG. 12 illustrates one embodiment of an anti-resonant element preform 300i where a first circular radius R_outer 320i of an ARE outer element 310i is less than a second circular radius R_inner 350i of an ARE inner element 340i;
The first circle radius R_outer is greater than 2 mm and less than 10 mm;
The second circle radius R_inner is greater than 20 mm and less than 30 mm;
The first central angle α_outer is greater than 210° and less than 250°;
The second central angle α_inner is greater than 48° and less than 70°.

The anti-resonant element preform 300i designed in this manner has the following characteristics:
the second longitudinal axis 341 is below the first chord;
The first longitudinal axis 311i passes through the exterior of the ARE inner element 340i;
The angle between the ARE outer wall 315 and the wall 345 is within [70°; 110°], in particular within [80°; 100°];
The ratio of the first segment height to the second segment height may be between 3 and 10.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 12.

FIG. 13 illustrates one embodiment of an anti-resonant element preform 300j where a first circular radius R_outer 320j of an ARE outer element 310j is less than a second circular radius R_inner 350j of an ARE inner element 340j;
The first circle radius R_outer is greater than 2 mm and less than 10 mm;
The second circle radius R_inner is greater than 20 mm and less than 30 mm;
The first central angle α_outer is greater than 270° and less than 330°;
The second central angle α_inner is greater than 15° and less than 35°.

The anti-resonant element preform 300j designed in this manner has the following features:
the second longitudinal axis 341 is below the first chord;
first longitudinal axis 311j passes through the exterior of ARE inner element 340j;
The angle between the ARE outer wall 315 and the wall 345 is within [50°; 130°], in particular within [70°; 110°];
The ratio of the first segment height to the second segment height may be between 28 and 44.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 13.

Figures 14 and 15 show various embodiments of anti-resonant element preforms in which the first circular radius R_outer of the ARE outer element and the second circular radius R_inner of the ARE inner element are essentially the same size.

FIG. 14 illustrates one embodiment of an anti-resonant element preform 300k where a first circular radius R_outer 320k of an ARE outer element 310k and a second circular radius R_inner 350k of an ARE inner element 340k are essentially the same size;
R_outer and R_inner are smaller than 7 mm, in particular smaller than 6 mm;
R_outer and R_inner are greater than 3 mm, in particular greater than 4 mm;
The first central angle α_outer is greater than 200° and less than 260°;
The second central angle α_inner is greater than 100° and smaller than 160°.

The anti-resonant element preform 300k designed in this manner has the following characteristics:
the second longitudinal axis 341 is below the first chord;
First longitudinal axis 311k passes through the interior of ARE inner element 340k;
The angle between the ARE outer wall 315 and the wall 345 is within [10°; 30°], in particular within [70°; 120°];
• the ratio of the first segment height to the second segment height is between 1 and 6.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 14.

FIG. 15 illustrates one embodiment of an anti-resonant element preform 300i where a first circular radius R_outer 320i of an ARE outer element 310i and a second circular radius R_inner 350i of an ARE inner element 340i are essentially identical;
R_outer and R_inner are smaller than 7 mm, in particular smaller than 6 mm;
R_outer and R_inner are greater than 3 mm, in particular greater than 4 mm;
The first central angle α_outer is greater than 270° and less than 330°,
The second central angle α_inner is greater than 30° and less than 90°.

The anti-resonant element preform 300i designed in this manner has the following characteristics:
the second longitudinal axis 341 is below the first chord;
The first longitudinal axis 311i passes through the exterior of the ARE inner element 340i;
The angle between the ARE outer wall 315 and the wall 345 is within [60°; 110°], in particular within [70°; 95°];
The ratio of the first segment height to the second segment height may be between 5 and 16.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 15.

16 shows a cross section of a preform 100 from which an anti-resonant hollow core fiber 2400 can be manufactured. The preform 100 includes a cladding tube 200 having a cladding tube inner bore 220 and a cladding tube longitudinal axis 230 along which a cladding tube wall 210 bounded by an inner surface 215 and an outer surface 216 extends. An anti-resonant element preform 300 is placed in the cladding tube. The preform 100 has a preform core radius R_preform 231 resulting from the shortest distance between the cladding tube longitudinal axis 230 and the anti-resonant element preform 300. In the finished preform, several anti-resonant element preforms 300 are placed at target positions on the inner surface 215 of the cladding tube wall 210, spaced apart from each other and in non-contact. Here, the preform 100 is provided to have at least one anti-resonant element preform 300 according to at least any one of the embodiments of the anti-resonant element preforms 300a-n listed herein.

16 shows a cross section of the preform 100 and clarifies the arrangement of the anti-resonant element preform 300 on the cladding tube inner surface 215. The anti-resonant element preform 300 is tubular in construction and therefore projects into the drawing plane. The arc-shaped ARE outer element 310 and the arc-shaped ARE inner element 340 are connected to each other along two connection lines 370, 370' arranged essentially parallel to the first longitudinal axis 311. These two connection lines 370, 370' are also connected to the cladding tube wall 210.

In the case of preforms known from the prior art, the ARE outer element and the ARE inner element are designed tubularly. This design has the disadvantage that the nested ARE outer element and the ARE inner element are in each case connected to each other and to the cladding tube along only one connecting line. There is therefore a risk that during stretching and/or crushing, the anti-resonant element preforms undergo a rotational movement, thus disturbing the uniformly distributed arrangement of the anti-resonant element preforms at the cladding tube inner wall, which is reflected in an increase in attenuation. In comparison with these preforms, the preform according to the invention is characterized in that the anti-resonant element preform 300 is connected to the cladding tube wall 210 along two connecting lines 370, 370'. This prevents a rotational movement of the anti-resonant element preform 300 in the cladding tube during stretching and/or crushing.

17 shows a cross section of an embodiment of the anti-resonant element preform 300m, characterized in that the ARE arc element 390 is disposed in the inner space 317 of the ARE outer element 310m and on the ARE inner element 340m. The ARE arc element 390 functions as a non-resonant element that damps higher modes. In this embodiment, the ARE arc element 390 is designed in a circular shape and has a radius R_circle 392 and a third longitudinal axis 395. Furthermore, the ARE arc element 390 is connected to the ARE inner element 340m along a contact line 393, in particular by material-to-material bonding. In one embodiment, the contact line 393 is disposed on the arc-shaped ARE inner element 340m such that the distance between the contact line 393 and the first chord is maximized.

In the design of this embodiment of the anti-resonant element preform 300m, the first circular radius R_outer 320m of the ARE outer element 340m can be smaller than the second circular radius R_inner 350m of the ARE inner element 310f;
The first circle radius R_outer is greater than 10 mm and less than 15 mm;
The second circle radius R_inner is greater than 12 mm and less than 18 mm;
The first central angle α_outer is greater than 270° and less than 330°;
The second central angle α_inner is greater than 30° and less than 70°.

Thus, for the ARE arc element 390,
- Radius R_circle 392 can be greater than 10 mm and less than 15 mm.

The anti-resonance element preform 300m designed in this way has the following characteristics:
the second longitudinal axis 341 is below the first chord;
- the first longitudinal axis 311m passes through the exterior of the ARE inner element 340m;
The third longitudinal axis 395 passes through the exterior of the ARE inner element 340m;
The angle between the ARE outer wall 315 and the wall 345 is within [35°; 100°], in particular within [45°; 90°];
The ratio of the first segment height to the second segment height may be between 13 and 19.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 17.

18 shows a cross section of an embodiment of the anti-resonant element preform 300n, characterized in that the ARE arc element 390' is designed in the shape of a circular arc and has a fifth circular radius R_arc 394 and a fifth central angle α_arc. Furthermore, the ARE arc element 390' can have a third longitudinal axis 395'. The ARE arc element 390' is connected to the ARE outer element 310n and/or the ARE inner element 340n along two contact lines. In particular, each of the two contact lines 393', 393" can be connected to a respective one of the two connection lines 370, 370' by a material-to-material bond.

In the design of this embodiment of the anti-resonant element preform 300n, a first circular radius R_outer 320n of the ARE outer element 310n can be smaller than a second circular radius R_inner 350n of the ARE inner element 340n;
The first circle radius R_outer is greater than 10 mm and less than 15 mm;
The second circle radius R_inner is greater than 12 mm and less than 18 mm;
The first central angle α_outer is greater than 210° and less than 250°;
The second central angle α_inner is greater than 90° and less than 115°.

Thus, for the ARE arc element 390',
The fifth circle radius R_arc 394 may be greater than 2.3 mm and less than 4.5 mm;
The fifth central angle α_arc may be greater than 160° and less than 230°.

The anti-resonant element preform 300n designed in this manner has the following characteristics:
the second longitudinal axis 341 is below the first chord;
- first longitudinal axis 311n passes through the exterior of ARE inner element 340n;
The third longitudinal axis 395 passes below the first chord;
The angle between the ARE outer wall 315 and the wall 345 is within [30°; 90°], in particular within [45°; 85°];
• the ratio of the first segment height to the second segment height is between 1 and 6.

Due to the size of the second circle radius and its resulting location in the drawing, the second longitudinal axis 341 is not depicted in FIG. 18.

In one embodiment, the ARE arc elements 390, 390' may in particular comprise an amorphous solid, in particular glass, in particular quartz glass, and the ARE arc elements 390, 390' and the ARE outer elements 310m, n may in particular be made of the same material.

19 shows a longitudinal cross section and FIG. 20 shows a cross section through the anti-resonant hollow core fiber 2400. A cross section of the anti-resonant hollow core fiber 2400 between two cut lines A-A and B-B is shown. The anti-resonant hollow core fiber 2400 has a coating 2450. In the illustrated embodiment of the anti-resonant hollow core fiber 2400, the coating 2450 is composed of an elongated coating tube 200 and an elongated coating material 2452. In the illustrated embodiment, the coating material 2452 and the coating tube material 200 are designed to be made of the same material, so the transition between the two materials is not marked. The coating 2450 has a coating inner radius 2465, which results from the distance from the longitudinal axis 2460 to the inner surface 2480 of the anti-resonant hollow core fiber.

The anti-resonant hollow core fiber 2400 has a hollow core 2470. Electromagnetic waves can propagate through the hollow core 2470. In the embodiment shown in FIG. 19, two anti-resonant elements 2410 are disposed inside the hollow core 2470. They are connected to the coating inner surface 2480 of the coating 2450 by material-to-material coupling. The anti-resonant element 2410 has an ARE outer unit 2420 and an ARE inner unit 2430. Inside the ARE outer unit 2420, the ARE inner unit 2430 is disposed. The anti-resonant element 2410 is disposed parallel to the longitudinal axis 2460 of the anti-resonant hollow core fiber 2400. The hollow core fiber 2400 has a core radius 2405, which results from the shortest distance between the longitudinal axis 2460 of the anti-resonant hollow core fiber 2400 and the ARE outer unit 2420.

20 clarifies the arrangement of the anti-resonant element 2410 on the inner surface 2480 that limits the hollow core 2470. The anti-resonant element 2410 is configured in a tubular shape. The anti-resonant hollow core fiber 2400 is provided with a coating 2450, on whose inner surface 2480 the anti-resonant element 2410 according to the invention is arranged. The ARE outer unit 2420 and the ARE inner unit 2430 are thus formed in an arc shape. The ARE outer unit 2420 and the ARE inner unit 2430 are connected to each other along two seam lines. These two seam lines are also connected to the inner surface 2480 of the coating. The ARE inner unit 2430 designed in an arc shape thereby protrudes into the inner space at least partially limited by the ARE outer wall.

Describe the geometric dimensions of the anti-resonant hollow-core fiber 2400:
The ARE outer unit 2420 has a third circle radius FB_outer 2422;
The ARE inner unit 2430 has a fourth circle radius FB_inner 2432;
The ARE outer unit 2420 has a third central angle β_outer 2423;
The ARE inner unit 2430 has a fourth central angle β_inner 2433.

The illustrated ARE inner unit 2430 and/or ARE outer unit 2420 may partially have a wall thickness in the range of 0.2 to 2 μm. In one embodiment, the ARE inner unit 2430 and/or ARE outer unit 2420 have a wall thickness of 0.25 μm to 0.75 μm, particularly 0.35 μm to 0.65 μm, especially 0.5 μm. The illustrated cladding tube 2450 may have an outer diameter in the range of 190 to 270 μm for a length of at least 1000 m. The inner diameter of the hollow core 2470 is preferably 50 to 100 μm.

By construction according to one of the embodiments, the anti-resonant hollow-core fiber 2400 has the following characteristics:
● Basic attenuation of less than 0.15 dB/km at transmission wavelengths of 1.0 to 2.5 μm;
- a fundamental attenuation of less than 1 dB/km at transmission wavelengths up to 0.8 μm.

In one embodiment, the anti-resonant hollow core fiber 2400 can have three, four, five, six, seven, or eight anti-resonant elements 2410. In particular, the anti-resonant hollow core fiber 2400 can have an odd number of anti-resonant elements 2410. In one embodiment, the anti-resonant hollow core fiber 2400 has a core radius that is smaller than 50 μm, particularly smaller than 40 μm, particularly smaller than 30 μm, particularly smaller than 25 μm, particularly smaller than 20 μm, particularly smaller than 15 μm, particularly smaller than 13 μm.

The ARE outer unit 2420 has a third segment height 2424. This third segment height 2424 describes the length of a straight line that is perpendicular to the chord and extends to the maximum height of the ARE outer unit 2420.

The ARE inner unit 2430 has a fourth segment height 2434. This fourth segment height 2434 describes the length of a straight line that is perpendicular to the chord and extends to the maximum height of the ARE inner unit 2430.

The illustrated anti-resonant hollow-core fiber 2400 has a Bolt circle radius resulting from the sum of the core radius 2405 and a third circle radius FB_outer 2422.

The illustrated anti-resonant hollow core fiber 2400 is manufactured from the preform 100. The manufacturing of the anti-resonant hollow core fiber 2400 from the preform 100 is performed in particular by performing one or more of the hot forming processes, i.e., stretching 2300, crushing 2100, and adding additional coating material 2200, one or more times.

One embodiment of the anti-resonant hollow core fiber 2400 is characterized in that the ARE arc unit is disposed within the inner space of the ARE outer unit, in particular, the ARE arc unit is disposed in the ARE inner unit. In particular, the ARE arc unit is manufactured from the ARE arc element by performing one or several of the following hot forming processes once or repeatedly: stretching and/or crushing.

Figures 21 and 22 show individual parts that can be used as part of a method for manufacturing a preform 100. The method thereby comprises the following steps (see also Figure 27):
a) providing 1000 a cladding tube 200 having a cladding tube bore 220 and a cladding tube longitudinal axis 230 along which extends a cladding tube wall 210 bounded by an inner surface 215 and an outer surface 216;
b) preparing 1100 several anti-resonant element preforms 300a-n, each including an ARE outer element 310 and an ARE inner element 340 inserted therein;
c) Step 1200 of placing the anti-resonant element preforms 300a-n at target positions within the cladding tube bore 220;
d) processing 1300 the assembly comprising the cladding tube 200 and the anti-resonant element preforms 300a-n through a hot forming process selected from at least one of stretching and crushing;

This method is
A relative internal pressure in the range of -10 to -300 mbar, in particular -50 to -250 mbar, is set in the cladding bore 220 in step d) "treatment"1300;
The ARE outer element 310 and the ARE inner element 340 are designed in an arc shape in at least one of the anti-resonant element preforms 300a-n;
- The two connecting wires 370, 370' are connected to each other and connected to the cladding tube inner hole 220.

This type of anti-resonant element preform has the advantages mentioned above.

In a known method, the fixing of the anti-resonant element preforms 300a-n is performed at the two front faces of the cladding tube 200. This is done by point melting with a manual torch. This results in soot or combustion products that are deposited on the glass surface. This generally affects in particular the front face of the cladding tube but also its inner face and the surface of the anti-resonant element preforms. Due to the complexity of the geometric shapes to be produced, a complete cleaning of the assembly is almost impossible.

To overcome these drawbacks, a positioning template 400 can be used having at least one centering surface 420 that cooperates in a self-centering manner with the first end 250 of the cladding tube 200 so that the anti-resonant element preforms 300a-n are positioned at the target positions in step c) "Placing" 1200.

21 shows individual parts of one embodiment of an assembly 110 of a preform 100 of an anti-resonant hollow-core fiber 2400 according to the invention. The assembly 110 comprises a cladding tube 200. The cladding tube 200 is tubular in shape. At least one anti-resonant element preform 300a-n is disposed on the inner surface 215 of the cladding tube 200. To this end, the following:
A step is performed of preparing a positioning template 400, the positioning template 400 having several passage openings 410 passing through the positioning template 400, each of the passage openings 410 adapted to guide an anti-resonant element preform 300a-n longitudinally, the positioning template and several cladding tubes 200 being made from the same material.

As part of the "attachment" step, the positioning template 400 is connected to the first end 250 of the cladding tube 200. The positioning template 400 thereby ensures placement of the anti-resonant element preforms 300a-n at their target locations.

22, a portion of the anti-resonant element preform 300a-n is guided through the passage opening 410 and protrudes into the cladding tube bore 220. The positioning template 400 is lowered toward the cladding tube 200 as part of the "placement" step. After non-active and/or active attachment of the positioning template 400 to the cladding tube 200, the assembly 110 including the cladding tube 200, the anti-resonant element preform 300, and the positioning template 400 is further processed into a preform 100 by a hot forming process selected from at least one of stretching and crushing.

The positioning template 400 used is designed so that the passage openings 410 for the anti-resonant element preforms 300 are always located at the same angular distance from each other, thus automatically obtaining symmetry. Furthermore, a gas flow element for gas flow is provided in the center of the disk. For example, rinsing or cleaning with gas as well as application of negative pressure are possible within the entire tube setup in the later process. The size of the holes can affect the gas flow through the core region and the anti-resonant element preforms.

To overcome the above-mentioned drawbacks, in addition to the positioning template 400 shown in FIG. 22, a second positioning template 500 can also be used, which has several second passage openings 510 passing through the second positioning template 500, each configured to guide the anti-resonant element preforms 300a-n in the longitudinal direction.

The following steps are thereby provided:
- attaching the positioning template 400 to the first end 250 of the cladding tube 200';
Mating the second positioning template 500 with the second end 260 of the cladding tube 200;
Inserting at least a portion of the anti-resonant element preforms 300 a - n through the passage opening 410 and the second passage opening 510 to position the anti-resonant element preforms in the cladding tube bore 220 .

This means:
the positioning template 400 has at least one centering surface 420, which cooperates with the first end 250 of the cladding tube 200 in a self-centering manner such that the anti-resonant element preforms 300a-n are placed at the target positions in a “placement” step;
the second positioning template 500 has at least one second centering surface 520, which cooperates with the second end 260 of the cladding tube 200 in a self-centering manner such that the anti-resonant element preforms 300a-n are placed at the target positions in a “placement” step;
In particular, in step d) "processing", it is placed at the target position.

The cladding tube 200 thus has opposing centering surfaces 251 at the first end 250 and a second opposing centering surface 261 at the second end 260. In the illustrated embodiment, the positioning template 400 and the second positioning template 500 are at least partially shaped in a frustoconical shape. The centering surface 420 and the second centering surface 520 are thus formed in a partially cladding surface shape. In FIG. 21, the cladding tube 200 is at least partially truncated in a frustoconical shape in the region of the first end 2450 and the second end 260.

In particular, the positioning template 400 and the cladding tube 200, and/or the second positioning template 500 and the cladding tube 200 are made of the same material.

22 shows step "insertion" of at least a portion of the anti-resonant element preforms 300a-n into the second passage openings 510 of the second positioning template 500. Step f) "processing" 1300 of the assembly including the cladding tube 200, the anti-resonant element preforms 300a-n, the positioning template 400 and the second positioning template 500 is then performed by a hot forming process selected from at least one of stretching and crushing.

The embodiment of the method is characterized in that in step d) "treatment", the anti-resonant element preforms 300a-n are thermally fixed in a flameless manner to the cladding tube wall 210. Prior point-like melting of the anti-resonant element preforms 300a-n onto the cladding tube 200, in particular the cladding tube wall 210, in particular by a manual torch, is eliminated.

Figure 23 shows a preform 100 including anti-resonant element preforms 300a-n made from the assembly 110 shown in Figure 22.

24 shows an assembly 110' that can be reshaped into a preform 100' by stretching and/or crushing as part of step f) "processing". The method required for this purpose comprises the following steps:
A/ Preparing a third positioning template 600, the third positioning template 600 having a number of third passage openings 610 passing through the third positioning template 600, each of the third passage openings 610 adapted to guide an anti-resonance element preform 300a-n in the longitudinal direction, the third positioning template 600 having at least one third centering surface 620.

To make the illustrated preform 100':
B/ A step of manufacturing a tubular closure element 700 is required, the closure element 700 having an active surface 710 in the region of the first end region 730 for cooperating, in particular for positive cooperating, with the third centering surface 620.

The illustrated assembly 110' has a funnel-shaped closure element 700. The outer diameter of the closure element 700 in a first end region 730 essentially corresponds to the outer diameter of the cladding tube 200. In the opposite second end region 740, the diameter of the closure element 700 is reduced to form an outlet 750. This outlet 750 can in particular serve to adjust the pressure ratio in the at least one anti-resonant element preform 300a-n and/or in the cladding tube bore 220, respectively, in or within the cladding tube bore 220.

The assembly 110'' further includes a first connection element 900 and a second connection element 910, whereby the first connection element 900 is disposed at the first end 250 of the cladding tube 200 and the second connection element 910 is disposed at the second end 260 of the cladding tube.

FIG. 25 shows an assembly 100″, which is produced based on FIG. 24 after going through the following steps:
C/ Linking the third positioning template 600 to the first end region 730;
D/ connecting the closure element 700 to the second end 260 of the cladding tube 200, in particular by using a second connecting element 910 to the second end 260 of the cladding tube 200;
E/ A step of pushing at least a portion of the anti-resonant element preform 300a-n through the third passage opening 610 to position the anti-resonant element preform 300a-n within the cladding tube inner bore 220, wherein the third centering surface 620 cooperates with the working surface 710 in a self-centering manner so that the anti-resonant element preform 300a-n is positioned at the target position.

In the illustrated exemplary embodiment, the anti-resonant element preforms 300a-n are held at two positions on the end side. On the one hand, the anti-resonant element preforms 300a-n are held at the first end 250 of the cladding tube 200 by the positioning template 400. Furthermore, the third positioning template 600 ensures further end side holding of the anti-resonant element preforms 300a-n. The positioning template 400 and the third positioning template 600 together ensure that the anti-resonant element preforms 300a-n are held at the target position within the cladding tube inner bore 220.

In step d) "processing", the anti-resonant element preforms 300a-n may be thermally secured in a flameless manner to the cladding tube bore. In particular, FIG. 26, which shows the assembly passing through an electric furnace 800 as part of step d) "processing", clarifies this step. The movement arrow 810 clarifies the direction in which the assembly 110' is moved into the electric furnace 800 (a flameless heat source) so that the preform 100' is produced.

By using the electric furnace 800, the manual torch process for clamping the anti-resonant element preforms 300a-n can be omitted. With the manual torch process, there are problems with combustion products and soot formation associated with the use of a torch. The condensation cannot be completely removed afterwards, so the preforms are further processed already with impurities. Thus, during drawing, blisters, inclusions, and later fiber breakage, among others, can occur. The use of a furnace eliminates the above-mentioned problems and allows for the production of clean preforms.

As part of step d) "processing" 1500, the anti-resonant element preforms 300a-n are placed in the cladding tube bore 220.
or the positioning template 400, 400', 400'' and the second positioning template 500, or the positioning template 400, 400', 400'' and the third positioning template 600, 600',
Otherwise, it is held together without any inter-substance bonds.

One aspect of the method is that precise joining of the cladding tube 200 and the anti-resonant element preforms 300a-n can be performed directly in the processing shop (e.g., a vertical glass lathe, etc.), and therefore only one process step is required for assembly and drawing of the entire preform.

The anti-resonant element preforms 300a-n, which are only diagrammatically illustrated in Figures 22-26, can be designed according to each of the described embodiments. For this purpose, reference is made to the corresponding description.

FIG. 27 shows one embodiment of a method for manufacturing a preform 100, 100′ of an anti-resonant hollow-core fiber 2400, the method 2000 having the following method steps:
e) providing 1000 a cladding tube 200 having a cladding tube bore 220 and a cladding tube longitudinal axis 230 along which extends a cladding tube wall 210 bounded by an inner surface 215 and an outer surface 216;
f) preparing 1100 several anti-resonant element preforms 300a-n, each including an ARE outer element 310 and an ARE inner element 340 inserted therein;
g) Step 1200 of placing the anti-resonant element preforms 300a-n at the target positions within the cladding tube bore 220;
h) processing 1300 the assembly 110, 100' comprising the cladding tube 200 and the anti-resonant element preforms 300a-n by a hot forming process selected from at least one of stretching and crushing;

This means:
A relative internal pressure in the range of -10 to -300 mbar, in particular -50 to -250 mbar, is set in the cladding bore in step d) "treatment"1300;
The ARE outer element 310 and the ARE inner element 340 are designed in an arc shape in at least one of the anti-resonant element preforms 300a-n;
● They are connected to each other along two connecting lines 370, 370' and connected to the cladding tube inner bore 220.

28 illustrates one embodiment of a method for producing an anti-resonant hollow-core fiber 2400 from a preform 100, 100′ produced in accordance with, inter alia, any one of the method steps 1000-1300 described above. The method comprises:
further processing the preform 100, 100′ into an anti-resonant hollow-core fiber 2400;
Further processing steps include the following hot forming process:
Crushing step 2100;
A step 2200 of adding additional coating material; and A step 2300 of stretching.
The present invention includes one or several of the above steps performed once or repeatedly.

In particular, during the manufacture of the anti-resonant hollow-core fiber 2400 according to any of the preceding embodiments from the preform 100, 100′ according to any of the preceding embodiments, in particular as part of the “further processing” step, at least one of the following transitions may occur:
Anti-resonant element 2410 is fabricated from anti-resonant element preforms 300a-n;
At least a portion of the coating 2450 is generated from the coating tube 200;
The ARE outer unit 2420 is made up of the ARE outer elements 310a-n;
The ARE inner unit 2430 is made up of ARE inner elements 340a-n;
A third circle radius FB_outer 2422 is created from the first circle radii R_outer 320a-j,m,n;
A fourth circle radius FB_inner 2432 is created from the second circle radii R_inner 350a-j,m,n;
A third central angle β_outer 2423 is generated from the first central angle α_outer 325;
The fourth central angle β_inner 2433 is generated from the second central angle α_inner 355;
The third segment height HF_outer 2424 is generated from the first segment height H_outer 328;
The fourth segment height HF_inner 2434 is generated from the second segment height H_inner 358;
- Seam lines are generated from the connection lines 370, 370';
ARE arc units are generated from ARE arc elements 390, 390'.
The sixth circle radius FB_arc is generated from the fifth circle radius R_arc 394;
Radius FB_circle is generated from radius R_circle 392;
The sixth central angle β_arc is generated from the fifth central angle α_arc;
• Contact seams are formed from contact lines.

All of the properties and characteristics described for the positioning template also apply to the second positioning template and/or the third positioning template, and vice versa.

All of the properties and features described with respect to the method also apply to the preform and/or anti-resonant hollow-core fiber, and vice versa.

Unless otherwise specified, all physical variables specified in the claims, the description, the examples and the drawings are determined under normal conditions according to DIN 1343. The statement "under normal conditions" refers to measurements under conditions according to DIN 1343. The features disclosed in the claims, the description and the drawings may be important for the various designs of the claimed invention either separately or in any combination with one another. Features disclosed with respect to the apparatus, in particular the preform, the secondary preform or the antiresonant hollow-core fiber, are also disclosed with respect to the method and vice versa.

29-30 show the results of a simulation of two embodiments of an anti-resonant hollow-core fiber. In the shown embodiments of the anti-resonant hollow-core fiber, the third circle radius FB_outer and the fourth circle radius FB_inner were of the same length (FB_outer=FB_inner). The following values were used for the geometry of the anti-resonant element of the hollow-core fiber:
Fiber 1: the third circle radius FB_outer and the fourth circle radius FB_inner are each 12.25 μm;
Fiber 2: the third circle radius FB_outer and the fourth circle radius FB_inner are each 15.75 μm.

Both fibers have six ARE outer units, each with an ARE inner unit disposed within it. The core radius F_fiber is both 17.25 μm. The core radius R_fiber is obtained from the shortest distance between the longitudinal axis and the ARE outer units. The bolt circle radius of fiber 1 is 29.5 μm and the bolt circle radius of fiber 2 is 2.33 μm. The wall thickness of each of the ARE outer and inner units is 0.5 μm.

The "confinement loss" (also called waveguide loss) of the fundamental mode at a wavelength of 1550 nm for both fibers is plotted in the diagram of Figure 29 over the "Bow ratio". Thus, the confinement loss represents the waveguide loss along the hollow-core fiber, based on the energy radiated radially. In contrast, the Bow ratio is defined as:

The bow ratio therefore defines the ratio of the two central angles of the ARE unit (and thus the ARE outer unit and the ARE inner unit) to each other.

As part of the simulation, the confinement loss of the fundamental mode was determined versus the Bow ratio, where β_outer was moved within the interval of 205° to 310°. The quantity of the fourth central angle β_inner was obtained from the difference of the third central angle β_inner at 360°. As shown in FIG. 29, the two fibers (Fiber 1 and Fiber 2) span the space for Bow ratios where the confinement loss is less than 10E-2 db/m. The Bow ratio for this space is:
- Greater than 1.5, especially greater than 1.6, especially greater than 1.7,
● Less than 3.2, especially less than 2.8, especially less than 2.5.

Fibers designed in this way and within the span parameter space solve the technical problems mentioned above.

From the listed bow ratios, β_outer can be less than 275° and greater than 210°, with the sum of β_outer and β_inner having a value of 360°. The parameter space for the third segment height HF_outer and the fourth segment height HF_inner is also as follows based on the given variables for Fiber 1 and Fiber 2:
HF_outer/HF_inner is less than 6.5, especially less than 4, especially less than 3.2;
HF_outer/HF_inner is greater than 1.7, in particular greater than 1.75, in particular greater than 1.85.

As mentioned above, to achieve fundamental mode behavior in the hollow-core fibers described herein, the goal is to keep the light travel distance as short as possible. To improve the fundamental mode behavior of the hollow-core fiber, an additional loss mechanism can be used for this purpose, in which the energy of the HOMs is coupled to high-loss modes in the ARE unit (ARE outer unit and/or ARE inner unit) by adapted design of the hollow-core fiber. This coupling can occur in two groups of modes:
It requires adapted transport propagation velocities of the ARE modes in the ARE units (ARE-outer unit and/or ARE-inner unit) and the HOMs in the core of the hollow-core fiber.

The coupling of phase propagation velocities can be influenced, inter alia, by the geometry of the individual components of the hollow-core fiber. In particular, the parameter "z/R" turns out to be important, which is defined as:

As specified, z/R is obtained from the difference between the third segment height HF_outer (see 2424 in FIG. 20) and the fourth segment height HF_inner (see 2434 in FIG. 20) divided by the core radius R_fiber (see 2405 in FIG. 20).

The effective mode index neff is plotted in the diagram of Figure 30 via the ratio z/R defined above for Fiber 1 and Fiber 2. The graph shows the relationship between the effective mode index neff and
Modes within the ARE outer unit ("ARE mode fiber 1" and "ARE mode fiber 2"),
The first higher order mode in the core (HOM1), and the second higher order mode in the core (HOM2).

Particularly effective coupling occurs near the intersection of the graphs of the ARE mode and the higher order modes (here the first and second). The energy of the higher order modes in the core couples to the lossier ARE mode. Thus, the higher order modes are attenuated in the core and the hollow-core fiber has fundamental mode behavior over a shorter travel distance.

Thus, in one embodiment, an anti-resonant hollow-core fiber is obtained, which has a ratio z/R of:
greater than 0.6, especially greater than 0.7, especially greater than 0.8,
- Characterized by being smaller than 1.4, in particular smaller than 1.3, in particular smaller than 1.2.

In particular, z/R is in the interval [0.8;1.2]. This parameter space for z/R provides a good coupling of the phase propagation velocities of the two modes.

To achieve low confinement loss of the fundamental mode, particularly less than 10E-2 db/m, as well as fundamental mode behavior over short fiber distances, one embodiment of an anti-resonant hollow-core fiber has a ratio z/R of:
- greater than 0.75, especially greater than 0.8,
● Less than 1.25, especially less than 1.2,
The third circle radius FB_outer and the fourth circle radius FB_inner can be characterized as being essentially the same length (FB_outer = FB_inner), FB_outer and FB_inner being smaller than 17 μm and greater than 12 μm, and the bow ratio being smaller than 2.8 and greater than 1.6.

Further examples of anti-resonant element preforms and preforms according to the present invention are as follows:

Below are provided examples of anti-resonant element preforms and preform dimensions. The invention is further described in an exemplary manner by these examples. The invention is not limited to these examples. The following abbreviations are used:

The "segment height ratio" of a given antiresonant element preform is calculated as the ratio of the first segment height to the second segment height.

Example V1
In this alternative embodiment of the preform, the boundary condition R_outer>R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V2
In this alternative embodiment of the preform, the boundary condition R_outer>R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V3
In this alternative embodiment of the preform, the boundary condition R_outer>R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V4
In this alternative embodiment of the preform, the boundary condition R_outer>R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V5
In this alternative embodiment of the preform, the boundary condition R_outer>R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V6
In this alternative embodiment of the preform, the boundary condition: R_outer<R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V7
In this alternative embodiment of the preform, the boundary condition: R_outer<R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V8
In this alternative embodiment of the preform, the boundary condition: R_outer<R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V9
In this alternative embodiment of the preform, the boundary condition: R_outer<R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V10
In this alternative embodiment of the preform, the boundary condition: R_outer<R_inner was satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner.

Example V11
In this alternative embodiment of the preform, the boundary condition R_outer=R_inner is satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner. In the context of Example V11, a statement that the first circle radius R_outer and the second circle radius R_inner are the same length is understood to mean that the lengths differ by less than 1.0%.

Example V12
In this alternative embodiment of the preform, the boundary condition R_outer=R_inner is satisfied and the following geometry was used:

The result is a preform that can be manufactured in an accurate and reproducible manner. In the context of Example V12, a statement that the first circle radius R_outer and the second circle radius R_inner are the same length is understood to mean that the lengths differ by less than 1.0%.

Dimensions of examples of antiresonant hollow-core fibers according to the invention are specified below. The invention is further described in an exemplary manner by these examples. The invention is not limited to these examples. The following abbreviations are used:

The specified "segment height ratio" of an antiresonant hollow-core fiber is calculated as the ratio of the third segment height to the fourth segment height.

Example F1
In an alternative to this embodiment of an antiresonant hollow-core fiber, the boundary condition FB_outer>FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F2
In an alternative to this embodiment of an antiresonant hollow-core fiber, the boundary condition FB_outer>FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F3
In an alternative to this embodiment of an antiresonant hollow-core fiber, the boundary condition FB_outer>FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F4
In an alternative to this embodiment of an antiresonant hollow-core fiber, the boundary condition FB_outer>FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F5
In an alternative to this embodiment of an antiresonant hollow-core fiber, the boundary condition FB_outer>FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F6
In an alternative embodiment of the antiresonant hollow-core fiber, the boundary condition FB_outer<FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F7
In an alternative embodiment of the antiresonant hollow-core fiber, the boundary condition FB_outer<FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F8
In an alternative embodiment of the antiresonant hollow-core fiber, the boundary condition FB_outer<FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F9
In an alternative embodiment of the antiresonant hollow-core fiber, the boundary condition FB_outer<FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F10
In an alternative embodiment of the antiresonant hollow-core fiber, the boundary condition FB_outer<FB_inner
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F11
In an alternative to this embodiment of the antiresonant hollow-core fiber, the boundary conditions: the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer = FB_inner);
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Example F12
In an alternative to this embodiment of the antiresonant hollow-core fiber, the boundary conditions: the third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer = FB_inner);
is satisfied and the following geometry was used:

As a result, a low-attenuation antiresonant hollow-core fiber was obtained.

Unless otherwise specified, all physical variables specified in the claims, the description, the examples and the drawings are determined under normal conditions according to DIN 1343. The statement "under normal conditions" refers to measurements under conditions according to DIN 1343. The features disclosed in the claims, the description and the drawings may be important for the various embodiments of the claimed invention either separately or in any combination with one another. Features disclosed with respect to the apparatus, in particular the preform, the secondary preform or the antiresonant hollow-core fiber, are also disclosed with respect to the method and vice versa.

100, 100' Anti-resonant hollow core fiber preform 110, 110' Assembly 200 Cladding tube 210 Cladding tube wall 211 Cladding tube wall thickness 215 Cladding tube wall inner surface 216 Cladding tube wall outer surface 220 Cladding tube inner bore 230 Cladding tube longitudinal axis 231 Preform core radius R_preform
250 first end of cladding tube 251 opposing centering surfaces 260 second end of cladding tube 261 second opposing centering surfaces 298 first circle 299 second circle 300a-n anti-resonant element preform 310a-n ARE outer element 311a-j,m,n first longitudinal axis 315 ARE outer wall 317 inner space of ARE outer element 320a-j,m,n first circle radius R_outer
325 First central angle α_outer
328 first segment height 340a-n ARE inner element 341a-e second longitudinal axis 345 ARE inner element wall 347 ARE inner element second inner space 350a-j,m,n second circle radius R_inner
355 Second central angle α_inner
358 Second segment height 370, 370' Connection line 390, 390' ARE arc element 392 Radius of ARE arc element R_circle
393, 393', 393" Contact line 394 Fifth circle radius R_arc
395, 395' third longitudinal axis 400 positioning template 410 passage opening 420 centering surface 500 second positioning template 510 second passage opening 520 second centering surface 600 third positioning template 610 third passage opening 620 third centering surface 700 closure element 710 working surface 730 first end region 740 second end region 750 outlet 800 heat source 810 movement arrow 900 first connecting element 910 second connecting element 1000 providing a cladding tube 1100 providing several anti-resonating element preforms 1200 arranging 1300 processing 2000 method steps 1000-1300
2100 Crush 2200 Add additional coating material 2300 Stretch 2400 Anti-resonant hollow core fiber 2405 Core radius (R_fiber)
2410 Anti-resonant element 2420 Anti-resonant hollow core fiber ARE outer unit 2422 Third circle radius FB_outer
2423 Third central angle β_outer
2424 Third segment height F_outer
2430 Anti-resonant hollow core fiber ARE inner unit 2432 Fourth circle radius FB_inner
2433 Fourth central angle β_inner
2434 Fourth segment height F_inner
2450 coating of anti-resonant hollow-core fiber 2451 coating inner hole 2452 portion of pre-coating material in coating of anti-resonant hollow-core fiber 2458 seam line 2460 longitudinal axis of anti-resonant hollow-core fiber 2465 coating inner radius 2470 core of anti-resonant hollow-core fiber 2480 inner surface

Claims (17)

An anti-resonant element preform (300a-n) for producing an anti-resonant hollow-core fiber (2400), comprising:
a first longitudinal axis (311a-j,m,n);
An ARE outer element (310a-n) designed in a circular arc shape and an ARE inner element (340a-n),
said ARE outer element (310a-n) and said ARE inner element (340a-n) are connected to each other along two connecting lines (370, 370') arranged essentially parallel to said first longitudinal axis (311a-j,m,n);
said ARE outer element (310a-n) has an inner space (317) at least partially bounded by the ARE outer wall and into which said ARE inner element (340a-n) designed in an arcuate shape at least partially projects,
said ARE outer element has a first circle radius R_outer;
said ARE inner element has a second circle radius R_inner;
the ARE outer element has a first central angle α_outer;
the ARE inner element has a second central angle α_inner;
The first circle radius R_outer and the second circle radius R_inner are essentially the same length (R_outer=R_inner),
The anti-resonant element preform has the following characteristics:
R_outer and R_inner are smaller than 12 mm; and R_outer and R_inner are larger than 0.5 mm,
An anti-resonant element preform (300a-n), wherein α_outer is less than 350° and α_inner is greater than 30°. The ARE outer elements (310a-n) have a first segment height H_outer (328);
The ARE inner elements (340a-n) have a second segment height H_inner (358), in particular:
The anti-resonant element preform (300a-n) according to claim 1, characterized in that H_outer/H_inner is smaller than 30, in particular smaller than 14, in particular between 1 and 6. The anti-resonant element preform (300a-n) according to claim 1 or 2, characterized in that an ARE arc element (390, 390') is arranged in the inner space of the ARE outer element, in particular, the ARE arc element (390, 390') is arranged in the ARE inner element (340a-n). The anti-resonant element preform (300a-n) according to claim 3, characterized in that the ARE arc element (390, 390') comprises an amorphous solid, in particular glass, in particular quartz glass, in particular consists of an amorphous solid, in particular glass, in particular quartz glass, in particular the ARE arc element (390, 390') and the ARE outer element are made of the same material. The ARE arc element (390, 390') is designed in a circular arc shape and has a fifth circular radius R_arc (394) and a fifth central angle α_arc;
said ARE arc elements (390, 390') are connected to said ARE outer elements and/or said ARE inner elements (340a-n) along two contact lines (393, 393', 393'');
The anti-resonant element preform (300a-n) according to claim 3 , characterized in that The ARE arc element (390, 390') is designed to be circular and has a radius R_circle (392);
The anti-resonant element preform (300a-n) of claim 3 , characterized in that the ARE arc elements (390, 390') are connected to the ARE inner elements (340a-n) along contact lines (393, 393', 393''). A preform (100, 100') for an anti-resonant hollow-core fiber (2400), comprising:
A cladding tube (200) having a cladding tube bore (220) and a cladding tube longitudinal axis (230) along which extends a cladding tube wall (210) bounded by an inner surface (215) and an outer surface (216);
a number of anti-resonant element preforms (300a-n);
The anti-resonance element preforms (300a-n) are arranged at target positions on the inner surface (215) of the cladding tube wall (210) in a spaced-apart, non-contact manner;
A preform (100, 100') of an anti-resonant hollow-core fiber (2400), characterized in that at least one of the anti-resonant element preforms (300a-n) is designed according to claim 1 or 2. A method for manufacturing a preform (100, 100') of an anti-resonant hollow-core fiber (2400), comprising the steps of:
a) providing a cladding tube having a cladding tube bore (220) and a cladding tube longitudinal axis (230) along which extends a cladding tube wall (210) bounded by an inner surface (215) and an outer surface (216);
b) providing several anti-resonant element preforms (310a-n), each including an ARE outer element (310a-n) and an ARE inner element (340a-n) inserted therein;
c) placing the anti-resonance element preform (300a-n) at a target position within the cladding tube bore (220);
d) subjecting the assembly (110, 110') comprising said cladding tube (200) and said anti-resonant element preform (300 a-n) to a hot forming process selected from at least one of stretching and crushing,
A relative internal pressure in the range of -10 to -300 mbar, in particular -50 to -250 mbar, is set in the cladding bore (220) in step d) "treatment",
the ARE outer element (310a-n) and the ARE inner element (340a-n) are designed in an arc shape in at least one anti-resonant element preform (300a-n);
- connected to each other along two connecting lines (370, 370') and connected to the cladding tube bore (220) ;
At least one of the anti-resonant element preforms (300a-n) is designed according to claim 1 or 2.
A method comprising: 1. An anti-resonant hollow-core fiber (2400), comprising:
a coating (2450) having a coating inner bore (2451) and a coating longitudinal axis (2453) along which extends a coating wall (2456) bounded by a coating inner surface (2454) and a coating outer surface (2455);
several anti-resonant elements (2410), each of which comprises an ARE outer unit (2420) and an ARE inner unit (2430), the ARE outer unit (2420) designed in an arc shape and the ARE inner unit (2430) being connected to each other along two seam lines;
the anti-resonant elements (2410) are arranged at target positions on the coated inner surface (2454) of the coated wall (2456) in a spaced-apart, non-contacting relationship;
the ARE outer unit (2420) has an inner space at least partially bounded by the ARE outer wall and into which the ARE inner unit (2430) designed in an arcuate shape at least partially protrudes,
said ARE outer unit has a third circle radius FB_outer;
said ARE inner unit has a fourth circle radius FB_inner;
the ARE outer unit has a third central angle β_outer;
the ARE inner unit has a fourth central angle β_inner;
FB_outer is smaller than 30 μm , larger than 5 μm,
FB_inner is smaller than 30 μm and larger than 5 μm;
β_outer is less than 350°, β_inner is greater than 30°,
The third circle radius FB_outer and the fourth circle radius FB_inner are essentially the same length (FB_outer=FB_inner),
An anti-resonant hollow-core fiber (2400). The antiresonant hollow-core fiber (2400) according to claim 9, characterized in that the amount of deviation of the third circle radius FB_outer from the fourth circle radius is less than 5% of the third circle radius FB_outer, in particular less than 3%, in particular less than 2%, in particular less than 1.5%, in particular less than 1 %. At least one anti-resonant element has the following characteristics:
FB_outer is smaller than 25 μm, in particular smaller than 15 μm;
FB_outer is greater than 10 μm, in particular greater than 12 μm;
FB_inner is smaller than 25 μm, in particular smaller than 15 μm ;
The anti-resonant hollow-core fiber (2400) according to claim 9 or 10 , characterized in that it has at least one of the following: FB_inner is greater than 10 μm, in particular greater than 12 μm. At least one anti-resonant element has the following characteristics:
β_outer is smaller than 345°, especially smaller than 340°;
β_outer is greater than 275°, in particular greater than 295°, in particular greater than 320°;
β_inner is smaller than 195°, in particular smaller than 180°, in particular smaller than 150°;
The anti-resonant hollow-core fiber (2400) according to claim 9 or 10 , characterized in that it has at least one of the following: β_inner is greater than 40°, in particular greater than 50°. At least one anti-resonant element has the following characteristics:
β_outer is smaller than 275°, in particular smaller than 260°, in particular smaller than 250°;
β_outer is greater than 210°, particularly greater than 215°, particularly greater than 220°;
The anti-resonant hollow-core fiber (2400) according to claim 9 or 10 , characterized in that the sum of β_outer and β_inner has a value of 360°. The ARE outer unit (2420) has a third segment height HF_outer (2424) and the ARE inner unit (2430) has a fourth segment height H_inner (2434), in particular:
The anti-resonant hollow-core fiber (2400) according to claim 9 or 10 , characterized in that HF_outer/HF_inner<30. At least one anti-resonant element has the following characteristics:
HF_outer/HF_inner is less than 6.5, in particular less than 4, in particular less than 3.2;
The anti-resonant hollow-core fiber (2400) according to claim 14 , characterized in that HF_outer/HF_inner is greater than 1.7, in particular greater than 1.75, in particular greater than 1.85. At least one anti-resonant element has the following characteristics:
A bow ratio greater than 1.5, particularly greater than 1.55, particularly greater than 1.6;
a bow ratio of less than 3.2, particularly less than 2.8, particularly less than 2.5;
An anti-resonant hollow-core fiber (2400) according to claim 9 or 10 , characterized in particular in that the confinement loss of the fundamental mode is less than 10E-2 db/m. The ratio z/R is
greater than 0.6, particularly greater than 0.7, particularly greater than 0.8;
less than 1.4, in particular less than 1.3, in particular less than 1.2;
11. The anti-resonant hollow-core fiber (2400) according to claim 9 or 10 , characterized in that